I would check to see if it is pre-wired and what for. We bought a 88 Class C, that the generator compartment had been used for storage, but pre-wired for an Onan unit with the start switch already in place as were the fuel lines and base plate. When I found used one it slid right in and was an easy hookup.
The Onan generator I bought was "new" with less than 10 hours that had been parked on the beach in Florida when the tide came in. The rear section with control board had been partially submerged and the generator was replaced by insurance. Took a chance and bought it for $200 from the Rv dealer who removed it. I had it checked out by an Onan service center in Indianapolis, all it took was the board, a small section of wiring harness and I bought an exhaust system all for around $500. At $700 it was a great deal for the 8-9 years we used it.