Tiny Update.
Just a couple of pics of the finished CG/CA18 Throttle body...really easy to make this fit.
I decided to make up a spacer that brings the CA18 throttle body upto the CG's TB height, so i could fit the aux air valve in the stock position.
Main thing is to rotate the CA18's throttle cam (probs the same for sr20) by 90ish degress iirc. You just need to cut a new keyway, in the pic its not set at the full 90ish this was changed later on...if its not set correctly you have slack in the throttle cable, so no full throttle and adjustment is impossible.
Apart from that only issue i had was the lack of throttle sensor (its was missing on the CA18 -- not sure if the stock one is compatible?), so i just made the CG one fit...a quick throttle cable hybrid bracket was made up, to keep everything stockish / compact looking.
The small catch tank is mounted in the engine bay (see pic -- I abandoned the plastic option as it wasnt air tight enough for my needs), just need a few hose connectors to finish installing.
Not sure on testing the differnce as i've got to solve the maf fitment issue first. 
