1200gx so the rxi throttles is 45mm and the rsi ones is 43mm. I'm looking at the 43mm throttles.

I'll choke them to what is needed, a lathe and a piece of Alu will sort that, just need to get hold of someone that is running 4 throttles and the sizes they are using.

Personally I can't see the reason besides ALu is cooler and will stay cooler than MS, but a little powder coating will fix this, even heat wrap afterward. Almost all OEM manifolds is cast iron, only custom made stuff is alu.