Replace old Onan 5000 with box store portable

It seems defeatist to do what the OP is thinking when the result is far less convenient than the original generator installation. Remote start, on board fuel supply, use of all existing wiring, etc is worth much more than saving a few hundred dollars by adapting something that may be acceptable, or not.

I might check some of the RV salvage places for a replacement ONAN if the repair cost is prohibitive. Possibly find one for about equal cost as the contractor models.