Sorry, in terms of oil I was thinking about the 28 year old 300/6 in my van, with around 600,000 miles on it. For anything else, I'd follow what StingrayL82 says.
Zinc additive -- absolutely, new or old engine, if you have flat tappets, for the reason StingrayL82 stated. (Most of us have flat tappets in our beasts.) Also increases camshaft lifespan.
Better sealing valves usually means increased piston ring blow-by, unless you hone and re-ring. Do a dry/wet compression test and a leak-down compression test. Those will tell you what you actually need to do, versus just throwing dollars at it. (On these older Dodge engines, excess oil consumption is usually due to valve stem seals. These can be replaced without removing the heads.)
These older motorhome engines are often good-to-go, due to being low milage.
RvFNG76 -- absent bad results from compression tests, I'd just look at replacing broken studs. If on the rocker arm shafts, it can be done without removing the heads. If block to head studs, I'd consider removing the heads, replacing the broken studs, using new head gaskets, and torquing in the right order and specifications -- WITHOUT rebuilding the heads.
