[C model]

Also get et the carb out and check the carb enrichment circuit for clogs, also make sure the choke is functioning properly, there should not be a lot of slack in cable.

 

[C model]

You need to change the shims for proper ones(thinner ones), valve clearance usually gets tighter, valve seat wears so the valves are not sealing(they are staying a tiny bit open). Exhaust valves are usually most affected. First You need to measure valve clearance with cold engine at TDC, then calculate which thinner shims You need to get to obtain the proper clearance. The oil is probably seeping from head cover gasket, not the head base gasket? When You do the valves check the gasket, if it is intact add a tiny bit of engine sealer on it all the way around.