340 oil pressure? Help

If it's a flat tappet camshaft, idling is the DEAD WORST thing you can do on a fresh build. Once started, you should bring RPM up to at least 2500 and vary it between 2500 and 4000 for the first 15 minutes, otherwise you risk wiping a lobe and destroying the camshaft and lifters.

When I am "new" to something......especially something that can cost thousands of dollars, I READ every bit of information I can.

Nobody berated you or was a dick to you brother. I gave you good information. It's not my job to be your mama and tell you bedtime stories. If you do somethin stupid, I'm gonna tell you. We've all done it. That's how I've learned my most valuable lessons.

No one else gave you the break in information that I did. I couldn't care less how you perceive my attitude. That's all in your inference. ....and you inferred incorrectly, btw.

Good luck with your endeavor. My advice was simple. If it ain't broke, don't fix it. ......and yours ain't broke.

Right, except it’s a roller cam!
So everything you said was completely irrelevant. No cam break in needed for a roller cam.

And yeah, you totally jumped all over the guy. And you’re totally wrong to boot, because you popped off without even asking if it was a flat tappet cam. Open mouth, insert foot.

Yeah I'm going to pull it and go with a high volume just for good measure. What weight do you run?

10-30w is pretty light, but it’s a brand new engine. With the plug out I’m not sure you’d even manage the pressures you’ve got, but it’s possible.

Check for the plug. If it’s installed and that wasn’t the problem, you can go 15-40w or 20-50w. Thing is, your oil pressure now is as high as it’s going to be. The tolerances should be as tight as they'll ever be with a brand new engine. So, if the plug wasn’t left out, there’s a chance you have fairly loose tolerances on that brand new engine.

I’d check for the plug, then try a heavier weight oil before I messed with the oil pump. Just see what you get first. Modern machining techniques usually give tighter clearances than what these engines had 50 years ago from the factory, so, it follows that you should see higher pressures than was normal in the 70’s. You may have clearances that are a bit on the loose side. Which isn’t necessarily bad, but it’s worth figuring out now. Talk to your engine builder, better to get it sorted while it’s still under warranty from the shop.