I have swap barrels and locks from percussion to flinters:The only problem you run into seem the older flintlock (locks) are a tad larger on the lock plate:I had a hawkens flinter and drop that that into a PA Hunter stock that was a percussion gun.I had another set from a hawkens 45 cal. and also drop iit into another PA Hunter stock again some small fitted may be required .I favor the PA Hunter stocksI also here the white mountain stock is the same.
The main thing are the barrels 15/16 need 15/16 stocks and so on for 1" barrel to a 1" barrel stock.
http://i15.photobucket.com/albums/a380/lonewolf5347/P1010007.jpg
the above set up is from a vintage 50 cal hawkens
http://i15.photobucket.com/albums/a380/lonewolf5347/P1040007.jpg
here my renegade 54 flinter vintage kit gun.