OK, first post!!
i dont usuallt have to ask questions about small blocks, but this one has me stumped!!!
First.. about me.. I built my first 350 in 1978 to replace a 250 6 cyl in a 1968 Camaro I bought for 300 dollars... was a CM (construction Mechanic) in the SeaBees.. NMCB 5.. and by 1988 was working for a chevy dealer as a truck mechanic during the day, and a performance shop building engines by night.. I am now retired.. having married a woman with college degrees that makes GOOD money.... I build engines and restore 4x4 chevys as a hobby income.

On to the issue...
Bought a 383... was told that they could not make it run right so they replaced it... Got the spec sheet with it.. not a bad build!! eagle crank and rods, Kieth black pistons, Canfield Aluminum heads etc etc...
A LOT of problems wit this engine as I pulled it apart...
First.. the chambers and exhaust ports had a thick layer of soot/carbon so they had WAY too much carb on it, or didnt know how to adjust it.. Cam was pretty hefty with approx 318 duration and 660 lift... didnt need that much cam.. pulled the main and rod caps, and they had installed standard Clevite bearings on the scat crank, that had radiused edges, so the bearings were ALL galled along the edges.. Oil pickup tube was an aftermarket bolt on tube in an M55HV pump.. ok... BUT, when I unbolted it.. it fell out of the pump.. as someone had GROUND the tube so it would easily slide into the pump.... Talk about buying someone elses screw up.... However, the price I payed for all couldnt have bought the heads alone...

I ordered the correct bearings, new rings etc etc... new oil pump pickup tube, new Lunati cam with a little less duration and lift than it had originally...
I put it all together, checking everything twice.. bolted it onto the stand and fired it up.. WOW, really sounds healthy.... except... as it begins to warm up.. temp hits about 120.. and the oil pressure suddenly starts to drop... I watch it go from 65 to 40.... 20.... 5... 0... I hit the throttle, Oil pressure jumped to about 25, then dropped again... in total, it probably took 30 seconds to go from 65 to 0...
I Pulled it apart, ordered new cam bearings, installed them, checked the plug under the rear main cap.. checked the rods and mains with plastigauge... Installed a NEW Melling M55HV, and put it all back together, bolted it to the stand and started it... same problem.. as it hits 110 to 120 on the temp gauge, the oil pressure suddenly starts to fall and does not stop...
I pulled the gauge, and hooked it to my 489... exactly matches the gauge in the cab... Pulled another gauge from the shelf and hooked it to the stand, and tried again... with the same results....

SO!!! I am befuddled, and looking for advice...
NO, i did not let it run with 0 oil pressure to check pushrods etc... I really dont want to toast the cam and bearings, so thats not going to happen. Just hoping someone has run into a similar issue... or asssit me to figure out what I am missing!!!!
ANY, input is welcome!!!! thanks!!!!