Lots of older Winnebagos are still on the road
Thats a D18 in the original OP's pic. Fits in a normal parking spot.
1969-1970: Some were based on a Ford 6 cylinder chassis
1970 - early 1973 (M300/M350/M375): 318 base with a 413 option (most were 413); points based distributor
Late 1973 - 1977 (M300 [RM300] / M400 [RM350] / M500 [RM400]): 318 base with a 440-3 option (vast majority are 440); Electronic ignition; model confussing years. Use both M400 and RM350 when looking for parts as many parts mfgs just used RM350.
1978 -1980 (M300/M400/M500/M600): 360 base with a 440-3 option
These Class A chassis' were used in Winnebago, Coachman and many others.
Use of Chevy P30 MH Chassis started around 74-75 (mostly Itasca line). There was a Dodge/ Chevy mix until Dodge went bankrupt in 79. Chevy from then on with a few John Deere / Oskosh (Ford 460 engine) thrown in during the late 80's / early 90's.
My 27' 78 Chieftain