You need the jets for a 750 engine. I would think for the /7 or /6 R75 would work best. But I don't think that this will keep you from starting. The R90 jets will work fine to get it going. They will probably make smoke after it warms up and even if not I wouldn't leave them in because the extra rich running washes oil off the cylinder walls. this is not a problem for right now though. Just make rejetting the carbs next, after getting started. and don't forget.
The carbs are actually the same. It's the jets that are changed to fit the engine.