I've read the procedure somewhere, for removing just the upper section of the drive to replace the drive bellows but I'll be darned if I can find it. Can someone steer me in the right direction?
Drain the 30W gear oil.
Remove the helmet pin, and tilt the helmet upwards and out of your way.
Loosen the worm screw from the AFT-most bellows band clamp.
Remove the clevis pin so that the vertical linkage rod can swing downwards. (DO NOT leave the linkage rod connected to the eccentric piston!)
Remove the two 3/8" hex nuts and the two 3/8" cap screws.
The transmission should now lift up, turn sideways, and be pulled out.
If it is stuck, just loosen the two cap screws a few turns and jack upwards on them.... this will break any seal that is preventing the transmission from moving upwards.
Any preferred source for the new bellows - part number? And "O" rings?
OEM are typically best.... although the Sierra is OK.
Look here for part numbers by engine model number.
https://www.marinepartseurope.com/en/volvo-penta-schematics-MarineGasolineEngines.aspx
Also, typically, which PDS assembly would I have for the 270 six cylinder engine - single or double bearing?
You will have the single bearing PDS with a pilot nose.