all rubbers from 36-carbed bikes would fit, GSX-R750 J/K, 1100 K/L, B12 Mk1, and probably a few others. But the 750 J/K rubbers will get the carbs positioned at the right angle/height, B12 ones won't, about 1100 ones I'm not sure.
Depends on air filter configuration, fuel tap placement, etc. If it's a stock 750 engine in a 750 frame I would think '88-'89 GSX-R750 rubbers would be fine.
shocks are better mounted on studs, not bolts. With bolts the forces on the thread are quite big and it can start unscrewing itself, once it's a bit loose it breaks easily. No such problems with studs. The nut at the end is just there for preventing the shock from moving sideways and the forces in that direction are almost zero. HD's V-Rod is a good example of how it should not be done.