Thanks for the responses. The three "O" size drives all used Renault four cylinder engines. These engines use wet liners. the 60 hp unit has a cast iron block, flywheel alternator on the front of the engine (towards the bow) and uses a pair of sidedraft outboard-style carbs. The 89 and 90 hp units have an aluminum block and a single downdraft carb. The main difference is that the 80 hp has a non-crossflow cylinder head and, usually, a manual crankup for the lower unit. The 90 hp uses a crossflow cylinder head and, usually, a hydraulic tilt. I've run my 90 a little, it works but has a rather bizarre cooling system intended to drain down like an outboard, and easily clogged with sand.
It appears that the exhaust bellows is available for around $45. A few places seem to have the drive shaft bellows for around $125. I'm thinking that if these are old stock the rubber may be stiffened up. The units can run without the exhaust bellows but if the drive shaft bellows tears or comes off the boat will be flooded.
My sense is that these units are fun to tinker with for the mechanically inclined but probably don't make a lot of sense for regular use. They are heavy for the thrust they produce, complex, not easy to work on, parts are scarce and expensive.... I guess there are reasons small outdrives aren't popular any more.
