oil pressure and crankcase pressure
Dartman has a point about the oil plugs in the block. I had an engine where the machine shop forgot to put a couple in and it took me 5 engine pulls before I found the problem. They left the two that go behind the camshaft thrust plate out and I could only get 25 psi cold on startup and went down to 10-15 warm. I can't remember where all of the plugs go at this time without looking at a bare block, but find out where they are all supposed to be and double check that they are all reinstalled before putting the block back together. Remember it is YOUR engine, not theirs. Don't let their mistake cost you engine damage.
Now what about the engine bearings. Are all of the oil holes properly aligned in the engine??? Misaligned oil feed holes can cause high pressure.
The main bearing shells have holes for the halves that go into the block for the crankshaft. Do not put the shell without the oil hole in the block. The shell WITHOUT the hole goes in the MAIN BEARING CAP.
Same goes for the conecting rod bearings, if they have oil holes to oil the cylinder bores, they must go into the rod, not the cap. The SHELL FOR THE CAP DOES NOT HAVE A HOLE IN IT. THE SHELL OPPOSITE THE CAP MUST HAVE THE HOLE, (or the one that goes into the rod gets the hole).
Also verify that the machine shop properly installed the cam bearings. Each cam bearing has holes for oiling that must be aligned with the holes in the block. Before assembling the short block, get a wire hanger and straighten it out. Stick the wire in each of the holes in the block for the main bearing shells and make sure that you can see the tip pass through the cam bearing into the cam bore (gently so as not to scratch your cam bearings). This will make sure that none of the oil feed holes from the crank to the cam are not blocked/obstructed. A general rule is that the holes should not be covered/overlapped by more than 50%. Or the hole should have at least 50% alignment or better. Next take the wire hanger and roll the block over and stick the wire into the oil feed holes on the head face of the block and check that the holes are properly aligned and not blocked. Over half of the hole should not be blocked, or reset the cam bearings for proper alignment.
I know it might be a little late to check these if your engine is assembled. This should always be checked before assembling the short block. ALWAYS CHECK YOUR OIL PLUGS AND BEARING HOLE ALIGHNMENT BEFORE/WHILE ASSEMBLING THE SHORT BLOCK! Just make this mistake ONCE, and you will never repeat it... Believe me..