Rajan,
To try and sum up everything, it appears you have a Parker Bros. 20 ga. V-Grade shotgun (i.e. a VH 20). The V = Grade, which is next to the lowest grade, with "Trojan" grade being the lowest. The H = Hammerless, which means it has no external hammers like the older models did. It also appears that you may even have a VHE 20 instead of a plain VH, with E = Ejectors. Ejectors were an upgrade option. A gun without Ejectors will have just a plain Extractor. The difference is that when you open the gun after firing, the Ejector will kick the fired shell (or shells if both were fired) completely free of the gun, with the spent hulls landing on the ground behind you. A plain extractor will simply lift the shells up out of the chambers about 1/4 inch when the gun is fully opened, making it easier for you to grasp them with your fingers for removal. Please note that if an Ejector gun has not been fired, it will function just like a plain extractor gun and simply lift up the UN-fired shells 1/4 in. for you to remove from the chambers with your fingers. You can quickly tell the difference between Ejectors and Extractors without disassembling the gun by simply opening the gun and looking to see if the part that lifts the shells is one piece that spans across the bottom of both barrels (extractor), or split vertically into left and right halves so they can operate independently on each barrel (ejectors). Also, just because it HAS ejectors doesn't necessarily mean they are original to the gun - there were companies that offered aftermarket installations of ejectors on Parker guns. Also, Parker themselves would retrofit ejectors onto a gun that originally left the factory with extractors only. Unfortunately, your gun's serial number is not listed in the Serialization book that many of us use to reference. There are gaps in the records, and your gun is in one of those gaps. If it were in the book, we could tell you the grade, gauge, original barrel length, and any options like ejectors, straight grip stock, etc. If your gun has ejectors and isn't stamped "VHE" on the receiver, then you will have to have a person who really knows what Parker factory ejectors look like examine the gun to determine originality. Even if they are retrofits, if done by the Parker factory it adds to the value of the gun over plain extractors. If aftermarket, it adds nothing, perhaps detracts some even.
Unfortunately, you can't use metric measurements on Parker guns to determine much since that is not the "language" they speak. The proper spacing between firing pin CENTERS is 1 inch on a 0-frame. You have to measure from the exact centers of each firing pin, not just the space between them. I suspect yours actually measures 1 inch, making it a 0-frame. Other frame sizes add 1/16th inch between centers as you go up (i.e. a 1-frame is 1-1/16 in. between centers, a 2-frame is 1-1/8 in., and so on). The 0-frame is the normal size for 20 gauge, although they can be found in 1-frame versions, and even 2-frame. For the most part, a 0-frame would be the most desireable for a 20 gauge for most shooters and collectors, with a few rare exceptions.
I understand what you meant by the 20 gauge comment, but it probably raised a few eyebrows around here. You are correct that the 20 gauge is an ideal gun for many women and the perfect gun to start a kid with, but many accomplished wingshots prefer to hunt with 20 or 28 gauge guns because of their wonderful handling characteristics in close quarters and snap-shot hunting situations. Come down South and hunt bobwhite quail behind pointing dogs and a 12 gauge will be frowned upon (maybe secretly, maybe openly, but not in a SERIOUS way because lots of people do it). Among most quail hunters, the 20 or 28 are considered the proper gun, preferably a side-by-side double like yours. Some really good wingshots actually look at shooting smallbores like the 20 as a badge of their prowess with a shotgun, analagous to a golfing handicap. If you go on a dove shoot and there is a guy who takes his limit with a smallbore 20 or 28 and doesn't waste a bunch of shells in the process, he will be secretly admired for his skills, whether the other shooters admit it or not. So you see, the smallbore can actually be a "macho" thing in the right hands, rather than the other way around. On the other hand, you mentioned home defense, and a 12 is definitely the way to go there and on the battlefield.
Regarding value - grade, scarcity, originality, and condition are the key determining factors. You have a leg up on the scarcity factor, because 20s are more "scarce" than the most-common 12 gauge. 28 gauges are worth more than 20s because 28s are even less common, and .410s are the least common and by far the most expensive. Originality means that no one has done anything to the gun other than normal cleaning since it left the factory. There are varying levels of originality due to repairs and modifications that may have been done to the gun by the owner(s) over its life. Many guns have been "restored" which means they are no longer original and not worth as much unless they were totally devoid of any original finish to begin with. A perfectly restored gun will never be worth what a similar gun with a decent amount of original finish remaining will be worth. Also, modifications like cutting the barrels shorter will seriously impact the value in a negative way. One way to tell if the barrels were cut is to look at the top rib that runs along and between the barrels on top. It has wavy lines cut into its top surface to help reduce glare. On most (but not ALL) original guns, these wavy lines stop about 1/8 in. from the muzzle end, leaving a bare, un-matted space right about where the front bead sight is. This is a good indicator that the barrels haven't been cut. However, some original uncut barrels have been seen with the wavy lines going right to the end, AND, some unscrupulous people have been known to fake the bare spot on a set of barrels that have been cut by filing the end of the rib. An experienced eye can usually detect this, however. The most common length for 20 gauge Parker barrels is 26 in., but 28 isn't uncommon, and 30 is occasionally seen. Anything longer than 30 or shorter than 26 is very unusual in 20 gauge. In fact, be suspect if they are shorter than 26, but there are a few original guns with barrels shorter than 26.
If you want to get an idea of the value of your gun, go on
www.gunsamerica.com and do a search for "Parker". Then sort through them and look for 20 gauge VH or VHEs, depending on which yours is. Try and find some that are in similar condition and originality and compare what they are asking. They might not bring the listed asking prices, but if you take an average you should get an idea of what the fair market value is.
Finally, thank you for your service to our country. Soldiers are always respected and welcomed here.
Jim