I have a fairly fresh rebuilt 73 440(under 2000miles on it). At times when driving at 55-65 mph the oil pressure will slowly start dropping. it will go from 60 to almost 0.when I let off the gas for a moment it starts climbing again.I'm thinking I need a breather in the valve covers since there are none. It does have a pcv vent to the carb.Do you think I'm on the right track or is there something else I need to check?

How much oil capacity ? .. grade of oil? .. oil temp?

I don't know if it will fix the problem but you need to vent the crank case. If you are drawing air out through the PVC valve, and it can't be replaced you will cause vacuum in the case. Usually pvc on one side and vent on the other.

Is the oil cold when it does this ?

What kind of gauge is telling you the oil pressure ?

If it is going down to almost ZERO(and is going almost 60 mph) ...and the engine is not making any strange noises ....

I say that the gauge is defective OR the sending unit is.

Check your pressure with a mechanical gauge.

A BB chev, just rebuilt in a pickup, was over at a mechanics house.. It had a horrible squeal that no one could diagnose.. Mechanic was just getting ready to pull the pan thinking the engine bearings were going out or were installed wrong.. Yes, it was making a horrible sound... I listened to it, and looked at it, then reached in and took out the oil "plug" in the valve cover.. No more squeal..

The pcv was pulling vacuum and the "plug" on the other valve cover was not letting in any air.. The whole engine was under vacuum and everywhere the engine could leak air it was.

God I felt good that day... A hero....

Thanks for the info.I think I'll replace the sending unit and mount a temporary gauge and see what happens.

But vent the one valve cover first. negative pressure in the crank case will cause O oil pressure

Will do.

Well?

Fram oil filter? Could be colapsing inside.

I would take off the oil pump regulator plug & give the plunger/spring a good visual or maybe sub in another pump (check clearances/clean it 1st). You would want a breather on one valve cover and the pcv to the carb base on the other valve cover. EDIT As said gauge & sending unit 1st