1. RXI throttles I think are too big. Look at motorcycle
throttles of size 36 to 38mm. The SU's are 38's.
2. Use aluminium. I have not seen one intake made of
normal metal and there must be a very good reason they
are all using aluminum.
3. Talk to kululadotgroen on the site. He explained in
detail to me how the different trigger mechanisms work
.He is also as I understand in the process to go crank
angle sensor.
4. Go 4 throttles not 2. It will give you better responce
and I think more power.

This info is not from personal experience but all the stuff I have read on the VW Forum. Those guys have tried some nice combination of stuff. Apparently the RXi throttles are too big for even the 2 liter 16 valve VW motors. They get better power from 40's or the RSi 43mm.
Your motor is 1400cc. I think it will perform better with a slightly smaller throttle. Check the bike stuff out to get a decent size.Let me also know what you come up with. I want to go bike throttles in the future but here in Bloem there are nothing.Will have to look in Jo'burg or in Cape where bike scrapyards are plenty full and hopefully at the right price.