I have a 1966 mustang coupe with a 289 2bbl. Several months ago, there
was a terrible clicking comming from the valve train. To my great
disgust, my oil pump had died. I replaced it with a high volume pump
(cheaper than the regular ones...go figure). I also replaced the
lifters and push rods. The heads were rebuild about 2 years ago, so
theyre still good. Now when i start the car, the engine sounds really
good and i have good oil pressure until it reaches operating
temperatures. The pressure drops until it reaches 25psi (20W50 oil to
compensate for failing rings) then it holds for about a couple of
minutes, then the pressure drops slowly down to 0 and smoke starts
spitting out the tail pipe at idle. There's no knocking and no ticking
so i assume the valve train and bearings are decent. Could it be the
high volume oil pump?

Ive had the car garaged for several months in hopes of saving up for a
rebuild. I start it up about once a month so it doesnt seize up on me
and every time it sounds beautiful and every time once it reaches
operating temps it does this. Any ideas that would hold off a rebuild?
Or anything i should look for when i do rebuild? Thanks!