[BadToTheBown]

The answer to your question is - it depends.

I don't know hardly anything about air heads and water boxers so I have nothing to say about them. Also, I'm not sure about the R1200C engines.

Oilheads - Yes and no. Within the R1100 engines, cylinders are interchangeable and have 99mm bores (this matters). If you want to put an R1150 cylinder (101mm bores) on an R1100 engine, you'll have to machine down the skirts that go into the engine cases (spigot holes) 1mm to fit. The R1150 engines have 1mm larger engine case holes so an R1100 cylinder should go in but then you'll have 0.5mm gap all the way around (no case support for the cylinder skirt). As to nathanmargolis point, IF you have a single spark, SJBMW sells an R1200RS conversion coil to use dual plugs (I've used their conversion for both my R11S bikes). If you have a dual spark, you might be stuck with keeping it dual spark.

Hexheads - Not sure about the cylinders (believe they are all 101mm bores), so maybe they should. I wonder if powder coating (silver vs. black) might be the reason for a different part number but honestly don't know for sure. The heads are different (as 2wheelmike points our) as are the rocker/cam assemblies on the R1200S. This doesn't mean you can't swap them, just that it requires more changes.

Cam heads - I think the HP2S are different than the others but perhaps someone like Shreddr will have a definitive answer. I believe the HP2S have different head stud spacing (can be overbored more) but can't say positively. I would be interested in this answer myself.

Good luck.