you need nothing mate.,
a t25 fits on and runs fine.

ive done it... so have many others :)

A T25 is a direct fit to your standard exhaust manifold, then you have the option to use a T25 downpipe or as has been mentioned you could try and use a T2 downpipe.

Engine management doesnt come in to it atall with a T25:)

it's a good idea to use something like an SAFC to fine tune the fueling. this will alow you to fit bigger injectors too