The most common motorhome powertrain in the mid-70's was a small block 400 engine and a beefed-up version of the TH-400 trans called a TH-425, I believe. It should have an odd-shaped oil pan about 2 1/2" deep, no kickdown cable, and a 1-wire electric downshift connector just above the manual gear select linkage. The way to identify the 400 engine is a BIG crankshaft damper with an off-balance weight cast into it. The flywheel/flex plate will have a weight on it, also. Good engine, IF you don't let it overheat. They're bad about cracking cylinder heads. The 400 MH engines had 4-bolt main bearings, IIRC.
Jerry
