The water pump bolts to the timing cover, not the block, though some bolts do pass all the way thru into the block as I recall. There are ~4 different timing covers for LA engines and I think all will bolt to any LA engine (I posted photos years ago). Indeed, the 5.2/5.9L Magnum timing covers may fit, but no need to go there. I don't think motor-home water pumps are any different than cars. I think there are only 2 types, the steel one (~1970 down) and the aluminum one. The lower radiator hose is on different sides. The aluminum one puts the fan connection ~1" further out, which causes issues w/ pulleys and radiator. You also need to consider the crankshaft damper since I recall thicknesses vary between 273 and 360. Also, read up on crank balancing. I recall most/all 360's had cast cranks and were externally balanced via the damper, so might not be able to swap. The 273 dampers also had 1 offset pulley hole. Even staying w/ the same engine and year, pulleys varied w/ accessories so can always take finagling.
