Replaced the fuel pump today.... Tried to get at it with the generator installed but decided that wasn't going to work out. Ended up dropping the generator using a floor jack and board to distribute the weight. This gave me a lot more room to work with.
Replaced the fuel pump with the Carter P4070 which did turn out to be an exact replacement. Everything bolted right up with no modifications except the power lines. The stock unit used nuts and bolts to attach ring crimp fittings while the new one had press on connections with pigtails and spring clamps. Cut off the rings and used butt splices to attach the pigtails with no problem.
Static fuel pressure is right at 5 psi. While running under full load the fuel pressure varies from 5 psi to around 3 psi. Ran the generator for about an hour with out a hiccup. The old fuel pump pressure would vary all over the place from 8psi to almost 0 back and fourth rapidly, so I think I'm in much better shape.
At least I know I can use a fuel pump that's not $280+. The pump I purchased was from an ebay seller. It was new and in the original box with all parts sealed in the original bag. Paperwork and warranty card included. Even if you don't find a deal like that they only cost around $85 from many suppliers. The original Onan pump had no markings on it at all except what looked like a serial number. Not even an Onan part number was attached. I suppose it possible that the Onan label had long since fallen off.
Well... Onto the next project. New AC Delco front rotors purchased from Rock Auto.