If you remove 1/4", that should eliminate the original crimp folds and leave you with a perfect hull for rolling. I do not have any data for the 12 gauge, so I cannot verify your load. Your payload of shot should be fine for upland birds. I use RST shells with 7/8 ounce of 7-1/2 shot in my composite barreled 12s. It is fine for the Ruffed Grouse. Good luck!

Yes prepping my area while awaiting the arrival of my newest addition I have looked for some data for shorter length hulls in 12ga as I plan on using this size for the roll crimper.

Not planning on using the same charge for a lighter load thats for sure I imagine I wanna go at least 1 or 2 grain less than normal.

If my line of thinking is correct, data for 2-3/4" hulls and 1 ounce of shot should be fine insofar as powder type and charge. Theoretically, you would, or may have to shorten the one piece wad to allow crimping, which might reduce your payload. There are specific tables out there for short shells, probably due to the wad issues after trimming your hulls. I have the info for my short tens, but nothing for short 12s. Search the forum. There quite a few good threads on loading the short 12. I don't want to confound you with what I DON'T know!

Yes I'm going to. I have looked at the Hogdon data center site and they didn't test what powder I'm using on their shorts. Just know that I'm going to keep looking and should I not find it my common sense is telling me just to drop a light charge, pattern test it and go from there.