While you have the transmission out, you should drain the antifreeze from the motor and replace the 2 freeze plugs in the back of the block if you haven't already done so. 2 brass freeze plugs are cheap, and will prevent much cussing if they go bad in 2 months! Sorry the rabbit hole got deeper. I had a 71 Challenger a few years ago, and the freeze plugs in the back of the block were leaking. I pulled the 904 out to fix them, and stepped into the rabbit hole! 2 freeze plugs turned into the 904 getting swapped for a 727, 7 1/4 rear getting swapped for an 8 3/4, new driveshaft, Comp cam, valve springs, Cloyes timing chain, TTI headers, aluminum intake, and new exhaust, 15" Rallye wheels to replace the cheesy body colored Cop wheels on it when I got it, and probably other things I have forgot! Damn the rabbits and their holes....lol. Good luck Doc.