Before the 1950s or 1960s major and minor engine overhauls were commonly done with OHV and flathead engines but it often involved a decision to overhaul or else buy a rebuild depending on the extent of work needed. Since you have an apparently experienced and inexpensive mechanic, an overhaul seems to be in order as a cost effective way to get on the road again. The rebuilt head,if done right, removes a lot of concerns. Make sure that the head rebuilder heats and flattens rebuilt ohc aluminum heads to keep the cam bearings in alignment rather than simply machining a warped head to flatness at the gasket surface. Yes, do the clutch as it is easy now and you will be good to go for a while with that. Don’t forget the pilot bearing if needed. The oil pump is likely good as is but if a new one is cheap, then ok. Some mechanics may get tired or will have time constraints and will recommend a scrapyard engine, a rebuilt or whatever. You might want to polish your crankshaft mains and rod journals with oil wetted emery cloth. Polish and frequently check with a micrometer to make sure that it is not being polished to out of round. Measure the crank to determine if you might want .001" or .002" oversize crank and rod bearing inserts if available.