i would stay away from the td manfold only because its a decent amount of work to locate and modify it and it really isnt a very good manifold.
however if you are on a budget it will work, u may also need a clutch but first thing you should do is go megasquirt, even without the turbo setup it will be a night and day difference because that air meter is terrible. in the long run an awesome budget motor build is to use the eta motor with a turbo deisel crank and rods and some forged pistons and a 325i head these setups can handle 500whp and would prolly only cost you 500 bucks if you can build an engine yourself.
i have a feeling 300whp will be good enough for quite a while, a 2600 pound car with 300whp and some good handling abilities is a blast.
btw 270whp on a mustang dyno is about 310whp in actuality, the dynojet dynos are much more accurate.