Re bottom-ends, that's what I understand too.
I have written responses from both Motoren-Israel and Siebenrock that the R75/5 power kit cylinders they sell don't require any changes to the motor, valves or carbs, which seems a bit strange - I would have thought that you would at least need to re-jet to suit the larger cylinders. The /5 power kit is specifically machined for that model so that no machining of the block is needed - ie. spigot at base of cylinders is 97mm, not 99mm.
I might just be being paranoid but before I lay out $1000 I'd like to know if it's going to work