Outboard engines are definitely worth looking at, good power to weight ratio, built to be held wide open continuously. Bit thirsty, but you can't have everything. A six cylinder two stroke won't have much torque fluctuation; easier on redrives.
A redrive needs to done carefully. It shouldn't take more than a few days work to have a solid design that's not far from optimum weight, if you work on design parameters established by others.
While the junkyard approach can be useful, it's probably going to be heavy compared to a custom solution. You may well find that an XYZ car wheel bearing happens to be just the right size. But you need to work out the loads and what size bearing you need first, or it's lucky dip. Could be solid but way heavier than needed, or you may lose your prop at the end of the runway...
If you don't want to work it out, I'd highly recommend reusing a design that has been proven. Or just buying one from a redrive guy.