Larry,
I had an O-290-D2 in my RV and loved that engine. However, the -G model is a bit of an odd ball and finding parts in the future will be a challenge. Some but not all the -G parts are interchangeable with the -D and -D2 engine.
If your engine didn't come with a carb, let me know, I have my -D2 carb for sale and it may work.
That said, I would run away from the O-290 dash anything. The reason is the parts availability. After my prop strike, we found that it would cost over $30K to do a major on the engine and that is because you are going to pay top dollar for the hard to find parts. Even then, we had a challenge finding someone who would even agree to overhaul the engine.
If you buy this project, I suggest you sell the O-290-G for whatever you can get out of it and put the money towards an O-320.
If I had a flying plane with a sound O-290, I would run that thing until it died and then replace it. This would give you time to find a good O-320 at a reasonable price.
Check out the engine page on my site, listed below, for the things I had to do to install the O-290-D2 on my RV-9.