You'll need one awesome, fan cooled tranny fluid cooler if you want the car to handle that kind of power. My 722.6 blew at 52K miles with 352rwhp and 366rwtq but the 722.4 should be a hell of a lot stronger than my weak 5spd tranny. The 97 722.6 was the weakest of them all, lol I found that out quick.
Twin turbos are easy and I know exactly where you need to pull the oil from and what to use. I didnt know **** about turbo's either until I did up my car, Im just a stupid 18 year old kid
. TT manifolds are easier to make as well
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Im not sure if you can get your power goals with the stock 10.5:1 compression. You may want to grab a spare piston and send it off to Ross or CP pistons and have them make a set to lower the compression.
There was a 500hp TT C36 several years ago. Search this forum section for the photos. I know they are in the Performance Paddock.