This is what I would do. Older freewheels just didn’t wear out like lightweight modern cassettes. If you did identify skipping in a particular SunTour freewheel cog, you could replace the worn cog instead of the entire freewheel. Accushift freewheel spacing was asymmetric (as stated by 70sSanO ).

Have you tried a new chain to see how it runs? 0.75 elongation is not bad.