i had a small block in my bracket car that did the same thing (318 or 360 i can't remember). i checked alot of things but never did find anything to blame it on. 1 old timer told me he had a ford motor do the same thing and after 3 rebuilds he discovered a crack in the lifter galley which would open some and bleed off presure with engine heat. of course there is no way to fix that so i would run the motor as is and start gathering parts for a backup motor if this 1 goes belly-up 3ddart

I have been pounding an LA motor for about four months almost daily (4.10's, 4-speed). It has about 20 psi at idle normal operating temp but goes to 15-17 when it gets over 200 F. At 6500 it is pumping ~65-70 psi. So far so good.

My 1969 340 Swinger, that I sold in 2001, had low oil pressure at idle, when the car was fully warmed up. Most of the time I had 10-12 lbs. at 750RPM idle, fully warmed up. One time the car was idling at 650, and the mechanical gauge read 8 lbs.!

The red oil pressure warning lamp faintly lit, but I jacked the idle to 950 and the lamp never lit again.

One area I was told to check but never got around
to was the pump pickup clearances, to the depth to the bottom of the pan, the angle of the tube, and the mating surface at the attachment point.

Engine never ticked, and the oil pressure increased as early posters stated, in a linear fashion to 50/60 lb.s at 60 MPH cruise.

The engine ran like that for 2 years, and I put a couple thousand miles on that engine, ran like a scalded dog!

The new owner also never had a problem, and he subsequently sold the car, and now ... still no problem!

Drive it and don't worry!

I had a built 340 in the Cuda and it had the same pressure that you described. Ran it for a lot of years and no problems. Now I have a built 408 in it with a HV pump...same oil pressure. I've ran this setup for a few years now and no problems. You have 10k miles on it now...don't worry about it.