I would sure get a EGT gauge on it after the rebuild if you don't have one. That engine must have been run really HOT to do all that piston damage. Running at or over 1250*F for an extended period of time will do the damage you have. Motor Homes are heavy, never ever lug them, always down shift, that keeps the EGT's down. Mountains are a *****. LOL
The EGT sensor should be installed in the exhaust manifold between #6 & #8 cyls.
The EGT sensor should be installed in the exhaust manifold between #6 & #8 cyls.