I think someone on another thread gave advice about the gearboxes (IB5) fitted on the 1.8 can only take 160bhp before giving up.
The 2 litre came with an MTX-75 which is a far stronger box in comparison. But i don't know if it is a straight swap.
And my advice would be to get brakes and suspension done before getting big power figures!

Wouldn't it save a lot more time and effort to buy an St170 for about £4500 save money on the mods and have 170(ish) bhp on tap, a better suspension option and bigger brakes. and you can work on from there?