Assuming your MH is over 25 feet long a "GM chassis", I'll agree with Gjac that you have a Chevy 454 (7.4 liter) on a P30 chassis. The P30 is further subdivided for replacement parts purposes into Base or Stepvan; motorhomes are a Base. Typically the engine would be carburated (naturally aspirated) with a Rochester Quadrajet.
The info you need for the engine/chassis is readily available online; get a GM or Chevy manual that includes the engine for that year and the year prior. Gulfstream wouldn't have any good info to give you anyway. They just build the stick-and-staple part on top of the delivered chassis.