The rev limiters are often set differently between the models.This is often published in the service manual. Normally the heads, pistons, cams, ignition are all the same. I think the Roadster has a different ignition.
This is my understanding also. There are differences in the gearboxes between 883's and 1200's.
If you mean gearing, then the 1200's are geared taller. However, the difference there is the sprocket, which can be changed. If you mean the actual transmission, then no the transmission are the same on 883's and 1200's. Although 04-05 had straight cut gear transmissions, while 06+ have helical gear transmissions. Now if you mean a difference in cam's, then 883's have different cams from 1200's in 04-06, but all 883 engines have the same cam and all 1200 engines have the same cam. In 2007+ both 883's and 1200's use the same cams.