i think if you want to use tbh you shoul use with high degree cams
on xe engine you cant use higger lift if you want to use you need pocket pistons
you need aftermarket ecu.

 

Depending on your budget - you can use a turn-key kit from http://www.sbdev.co.uk/Main.htm where I bought the 208hp kit for my Chevette - it's fairly expensive but comes with everything you need. It's also a good basis for later modifications as they should be able to supply suitable maps for uploading.
There is also http://www.qednet.demon.co.uk/ who have parallel throttle bodies and some other nice stuff (I lust after the alloy block!).
If you go for motorcycle throttle bodies, you may be able to fabricate your own or use http://www.boggbros.co.uk/ who have something of a name for building custom manifolds.
SBD and QED do kits so it's pretty much a simple spanner job but fabricating one will be a lot more work.
Initially, you're looking at around 20-30hp (estimates differ) with more torque as well - however, their real benefit is when you start modifying the car with head and cam' work.
Oh, and they sound great as well!

Forgot - with RHD vehicles, the master cylinder is in the way and will require some re-engineering with, perhaps, an internal pedal box - but I believe LHD vehicles are free of that hassle. It would pay to check!