Since we're talking motor home, are you wanting to be able to run regular pump gas, at the nominal 87 octane range? If so I would think that you're going to be looking at maybe a new cam with the "RV Grind", and keeping your compression where it is. Unless you're OK with pulling up to the premium pumps at every fill-up you're not going to have a lot of options beyond keeping it tuned, improving the flow (exhaust, maybe heads), camming it for mid-range torque and picking rear gears to put you in your power band up to cruise rpm's. Too much boost is going to push you to higher octane fuel, and still with single digit mileage, I expect.

The better option might be to consider a take-out engine/tranny/ECU package from a newer truck with a more modern ECU, better injection, more tranny speeds, etc, etc.