Are you running one or two pickups from the pan? I assume that your oil pump cover has a pickup. I ask because I went out to the shop and looked at the 540 and the 500 and how I have them plumbed. The 500 has a 2 piece Indy maxx pump cover that will allow 2 pickups, but I am only using one. The 540 is using the front entrance like the one you tried to hook the accumulator to. I was using a plate under the pump (have to use a longer driveshaft) but the stack interfered with the K frame with the motor plate I had. Both of these seem to be working OK so far.

When I was building that 540 (mega block) I obtained a used Milodon 21000 2 piece pump cover that has the AN-10 inlet thinking I would use the bottom plate and the cover to feed the pump from both sides if I had feed issues. Both of those pieces are on the shelf now. That pump cover is about 1" think and it could be drilled/tapped for a fitting on the outside that would tap into the outlet side of the pump. Maybe even an AN-10 if you placed it in the right place to clear the bolts. Smaller would fit even better.

Looking at the pics of that block you do not appear to have many other options if you want a AN-10 line to the accumulator. PM me if you are interested in either of these pieces, priced right. I also have the pickup. Looks like this one but the cover is hard anodized.

http://www.jegs.com/i/Milodon/697/21000/10002/-1

Under pump feed plate is shown in this pic:

https://www.carid.com/milodon/swivel-connect-mpn-21150.html