Rick,
The "Book" indicates your Parker left the factory as an 1886 Grade O with Plain Twist 30" barrels and capped pistol grip. I'm not being flippant by the following: I have never had my barrels measured for wall thickness. My thought process has been if there is pitting visible it is unlikely the barrels have been messed with and I try not to over think it. Many of my Parkers have bore in the .734 range as well. I have an 1881 Twist Steel Parker with light pitting and .751 bores I shoot all the time with AA hulls, 1oz, Win 209, 19.5 WST, WAA12SL @ 1180 and 7,400 psi. That is the same as AA Xtra-Lite target load. In fact I will shoot most anything off the shelf that is 1oz and under 1200 fps. Most shooters here are more clever and affluent than I and shoot
http://www.rstshells.com These shells have appropriate velocities and pressures for old stocks, Damascus and Twist barrels. I'm 72 and like you I had been warned of the dangers of Damascus all my life. It was with trepidation I started shooting them with Federal paper hulls and IMR 7625. A load Ross Seyfried had published in Guns and Ammo sometime in the 1980's. Good luck and have fun.
Kindest,
Harry