That looks like a good collar to fit a wet nitrous injector or additional fuel nozzle. Tuff part is going to be getting it to fit with the existing elbow, as you well know, it's really tight.

Would it be easier to design a different elbow out of aluminum with a tighter radius and an extended collar to fit an injector and move the 02 sensor up a little bit to prevent any over-spray from the added injector (nitrous or otherwise).

Cheers