I was told, it was a pressure supply port, but we could not get pressure from it, so the assumption its a suction port could be inferred, I guess. I have no other current way to get an AN10 line to attach to the block right now, so the accumulator is on the shelf for now.

Does the Indy block have oil pressure ports on the rear like a stock block, that would be the place to plumb ... unless the ports are supplying oil to the heads ?