416 low oil pressure at idle

Years ago i needed a new block for my son's car and we found a 340 block in Orange County that had a standard bore. We got it cheap at $65, in the late 80's. Rebuilt everything and when it would warm up it would go down to 5-10 psi. I tore that engine down twice going from the bottom up and I couldn't find it. The third time I went from the top down and when I grabbed the first lifter to pull it out it wiggled significantly. I had to find a spec book to find the normal lifter bore which is the .904. Well, our lifter b ore was a .912 factory oversize. I called every lifter maker in the country and no one had or would build me a set to fit the .912 bore. I finally determined that Mopar still had a few of the things in inventory. At the time there were 52 and cost $16 each. Finally got the dealer to sell me a set for $9 each. Naturally cured our problem. I discovered that the front pad on the block is marked with an "iron cross" stamping if they came oversize from the factory. I calculated that the clearance around the lifters was equal to a 1/2" hole in the oil system. A lot of oil will go through a hole that size. I still have that block and have not been willing to spend the money to get it bushed or resized. I guess I just have a good boat anchor. Max