Breaking in engine... oil press seems low...

I'm sure my engine builder took care of it. I looked everything over carefully when I got it back from him, and everything looked in order.

You can spot-check the general health of your engine by cutting open the first oil filter. See what is in there. I cut mine open with a good sharp utility knife. On a normal break-in you will see some stuff, it looks like metal flake paint in the oil. You can swirl it around in the bottom of the filter can and look at it and say "Hmmmm.... interesting."

Too much metal flake stuff... or big chunks of stuff..... and you know right away you need to pull the engine back out.

I cut my filters open regularly. On the 3rd filter after break-in, there was no more stuff, just oil.
Yeah, I was planning on taking a look inside the filter for sure. Here's a question - just how exactly do you go about checking the impeller to oil pump cover clearance with a plastigage?
Locate a primer tool and check the pump pressure. If that check ends up
without positive results, it's time to contact the engine builder for a consultation. Good Luck...
Good question that hinges on how fast the pump can be turned.
To determine if the pump is the problem, pressure should be better than whatever the reading you are getting.
Plug a guage into the turbo feed line and cross your fingers.
I have a PreLube System and my #'s with cold oil are 45/50, and 30/35 hot (with the pump modification and the heaviest spring) using Rotella 15/40.
If this is a new setup, you most likely have a problem that can be corrected
pulling the front cover and having a eyeball view of the situation.

I WOULD consult with the builder, before getting too far along with this little exercise. This is NOT your problem yet but it will be if you fail to have a visit and at least let him understand you are having a situation and that you would like his input... (and if he's worth his salt, he'll be pulling with you to get things corrected)... Good Luck
Before you assembled your pump, did you port the front cover? This is outlined in the Buick Motorsports book. The book claims that every 90 degree turn drops 10 psi pressure. The modifications outlined, knock the sharp edges off the 90 degree turns. You can make the same mods to the front covers with longer gears.

I am running a stock pump, with the mods, a wear plate and adjustable regulator plug. I have 15-20 psi hot at idle (900 rpm) and instant pressure response with RPM. The adjustable regulator only works at the high end not at idle.
I didn't know about the front cover port mod. If I end up taking it back off, I'll definitely have to look into doing that. Thanks!

Oh, and I still need a little bit of info - would someone please describe how I am supposed to go about getting measurements with a plastigage? I understand the basic concept, but how am I to know if the clearance is too much / what am I looking for? Thanks again!