my 68 is recieving a rebult performance 327 this summer (im doin it my self) and the 2 spd isnt as quick or robust as id like it to be. the 350 donor engine (stock rebuild to keep the car on the road) has already got the tranny knocking in park and neutral (!? that could be the answer right there yes?). the 327 is the #s matching engine if you were wondering why i would step the cu.in.s down. 327 will have less than 350 hp. what do rebuilt TH350 or TH400 trannys go for? thanks.