I just ordered a Gen1 Marauder trigger from Pyramyd Air. Plan on putting it on my 1720T so I've looked into it somewhat. I think it'll work with a thin spacer. Discosrus used to sell them and you can still check out their website to see what it looks like.No idea where to get the Challenger stock. Maybe call Crosman?Is your AR2078 stock modified to fit the 1720T? I actually have a couple QB78 thumbholes and have thought about making one fit my Disco.