it wont last at 400 i can tell you now, may people try to get away with it and it always ends with rods and pistons the wrong shape. Dont forget these car are now 20 years old so not alot new is doen that hasnt been done or tried before.
6 speed form any year will be fine at that power level, its gonna be more about getting it to fit, widetrack will mean hubs etc all bneed to be done as well and iirc the driveshaft is the wrong length for a classic.