I follow all threads on this forum, daily, hourly, minute by minute on some occasions. :lol:
I'm not an engine guru but whatever hours are on the parts you mentioned are also on the main bearings and camshaft bearings. Whenever I rebuilt a small block Chev engine back in my wild and crazy days, the block got all the frost plugs removed before boiling it in a hot tank and then new cam bearings and frost plugs were installed along all new main and rod bearings for the crankshaft.
I'm surprised that so many people who rebuild their air-cooled engines leave the old bearings in place. Yes...they are ball-bearing races but if those lasted forever, then how come we put them in the snow blowers and mowing decks all the time? Sure, they are receiving constant lubrication but an engine is something you use every time you start the tractor. Decks and blowers only get marginal use by comparison. New is new... old is used and perhaps...well-used.