I had one of those blocks, I think they were early Pro Stock Truck or Craftsman Truck blocks. I think the most easiest way will be running a single stage external pump with a pick up plumbed in to the oil pan. There are several pumps to choose from, Moroso, Petersen and Stockcar Products to name a few.

If you are planning on doing away with the aluminium main caps, changing over to a steel cap with provision for an internal oil pump could be done at that point. Then you could have someone like Harshman Automotive drill the block for you. Shadydell did some of the drilling for me on my block. I remember being quite annoyed about that, because I didn't ask for it to be done.

Best of luck with whatever you decide to do.