Looking to swap out my v6 and will probably end up with about 600 crank HP. I'd like to stick with a manual trans but would consider an auto if the sticks are too expensive.
Built T-5? Would a WC T-5 be ok or would I need a built one?
T-56? Would a stock T-56 take this? My brother's cobra puts out about 650hp and he says his trans would be good to 750. Are the GM T-56's the same?
TH400? how much power are these good for?

Also, what rear should I go with to handle that power? Woudl a 9" or a 12 bolt be cheaper?

 

The T56 will hold. The weak link is the output shaft. Be careful when launching on drag slicks.
If you have fabrication skills, the Ford 9" is far cheaper.

 

you can get a bolt in housing and axle package for the 9" from moser for about a grand, grab a stock center and you have the cheapest strong rear out there.

tranms depends on what you want, auto or manual. auto, a built th350 or th400, stick, a lt1 style used t56 would be the way to go, it wont last long behind 600 ft/lbs though. A tko600 5 speed will hold the power, but they are hard to find used and are about 2500 new.

 

A good rebuild on the T56 and it should hold. 87_TA has been running a T56 on his 406 motor for years and its held up. HIs motor is well over 600hp on spray and about 575 on motor I'd guess. It traps 130 mph now on motor and should go into the 140's on spray. Has been 138 on spray with old combo that was slower on motor.