Hey John;
A few things here.
1) I been thru many different out drives OMC, Alphas and now VP 280s w/ re-sealing and re- gearing including my volvo DP 280. My experience is that if your re-sealing just mark all your nut postion prior to disasemble and clean up, install seals, shims just like they came out and reset nuts down plus a little torque. With the re-gearing you really need to check end play and shim as necessary as your adding possible different dimension parts..
2) Regarding the parts exchange of gears, its very possible that both units use the same exact gears and MPE should know that information. I pretty much deal w/ those guys all the time when these situations arise. There GOOD. Gogswells, also have been very helpfull to me in the past. Your doing the right thing thou by getting down your rescources and info.
PM me and we can talk more in detail.
Mike