just purchased fuel milage horrible

I worked on a 351 from about the same era that someone had removed the emissions from and it had a similar problem. The emissions are engineered into the engine and you can't just remove them without causing problems. The person who modified the 351 had drilled out the plugs that were inserted into the carb adjustments and backed the needles all the way out. His thinking was that more fuel meant more power. he had also disconnected the vacuum advance from the distributer. The guy had also removed the thermostat to make it run cooler. All of that resulted in an engine that got miserable mileage and had no power.

I would say it's time to take the motorhome to a good mechanic who understands older engines. The 460s were fuel hogs, but they should be getting closer to 8 mpg.