Since it's an 8.1L engine, I'm guessing we are talking about a Workhorse chassis. Is it a P32 or the larger W22 chassis? Both use the 8.1L GM engine.
Engine access in a gas-chassis motorhome is always problematic. You need to be a contortionist and have an array of socket extensions and universals. Some may be reached from underneath, some on top, and some cylinders may be darn near impossible to get at.
Have you figured out how to remove the "doghouse" engine cover in your Newmar coach? And is there an access door out front, below the windshield? You didn't mention a coach model so we can only guess at what sort of bodywork you are dealing with.