farmall quirk? more like 'worn out' old engine quirk.
as the main bearing and rod bearings and cam to bore wear, the clearances open, thus more loss of oil pressure. add to that the pump itself wears.
the oil you use may be a factor as well, event he age of the oil, as the oil ages it gets fuel mixed and can thin.
if you are running a 30w or 10w30, my advice would be to go to a 15w40 or 20w50 oil. I'd try 15w40 first as it is a c rated oil, and is a really good product.
ideally you need a minimum of about 6psi of oil pressure per 1000 rpm. those 'zone' gauges don't really tell you much. I would swap in a 9$ sunpro gauge and see what your oil pressures are at hot and cold idle and throttle, then remember those numbers and compair them to your zone style gauge.
at idle you are running what? 500 rpm or maybee a bit less.. thus you can see why just a bit of positive pressure keeps her from knocking...
I know many ford n that at 500 rpm have 4-5 psi hot idle oil pressure and otherwise run fine..
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while it is worn and would likely benefit from some work, if you can keep the oil pressure normal using a 15w40 or 20w50 oil.. it won't hurt it to do so.
if you feel up to it, many times you can make a few psi oil pressure gain by simply dropping the oil pan, and pulling the main and rod bearing shells, seeing what size thay are and rolling that exact same size back in. the new shells will be less worn than the old, and you won't need to plastigauge them to see if they fit, as you know that whatever came out was fitting when new.
just the new bearing shells alone should pick up some oil pressure.
you could always rebuild the pump if you were inclined, and then even ream the ridge and hone the cyl and install new rings and then hand lap the valves too
watch out.. that poor mans rebuild I just talked about can lead you into a days work.. though is very cheap.. just bearing shells and rings and some tool usage. usually adds another 10ys or so of usefull service to a machine in the way of an oil pressure increase and some compression increase. I like to call the bearing shell replacement a poor mans 'lower' and the new rings and reaming the ridge and honing the cyls, and the the hand lapped valves a poor man's upper. also remember that if you repalce rings that you must ream the ridge on the cyl or it will break the new rings. I'd also lightly hone the cyls to make some crosshatching. remember to clean out any grinding compound from the valve areas too.
soundguy