I've rebuilt 4-5 of the Onan's on Miller Welders. If yours has an oil filter it is probably an Onan Performer. If no filter it is a CCK.
IIRC the crank can be turned .040 under but I might be thinking about the cyl bore.
You are not going to get a replacement engine cheaper than repairing yours if you are looking at new. And then you will need the engine adapter.
If you look around there are a lot of RV generators from scrapped RV's. I just bought one on craigslist for $160. that has the control PC board missing. These gens run at 1800 RPM so the engines last forever.
The crank is also tapered so a regular engine won't work, it has to be a generator version. The gen has no bearing on the engine end.