I have a 73' camaro and i'm in the process of swapping my turbo 400 for a m-20. Can i use my driveshaft? do i need to relocate my crossmember at all or should it just go in?

Welcome to the Club! I believe the M20 is a shorter case (overall length) including the bellhousing than the TH400, even if its 6 inch tailshaft housing. So, driveshaft would have to be lengthened, or buy one from a TH350 equipped car. There should be extra holes to move the crossmenber, one would have to check.

Maybe others here will respond.....

the crossmember should just slide forward, as the M20 will use the same mounting location as a TH350- which is what most second gen F bodies had. also, a driveshaft should be an easy $10 boneyard score- they are all over the place, as very few of those cars had the TH400. i don't know which output shaft the M20 has, but you MIGHT need to use the TH400 yoke on the new drieshaft.