I had a pretty bad rear mail seal leak and the engine oil pressure was on the low side. Decided to replace the oil pump at the same time. biggest chore was getting the pan off and back on, it was a very tight fit between the bell housing and front differential. I put the rig on jackstands, disconnected the shocks and let the axle sag as far as possible.
The install of the oil pump was very easy, would have been better to pull the distributor first (it was tricky lining up the oil pump drive with the dist. shaft). I followed Moses' instructions using a 1/2 cordless drill and an old screwdriver (removed the wooden handle, cleaned it up on a wire wheel and ground three flat spots to help the chuck grip the shaft). It was a little trickey keeping it centered in the dist. drive hole so using a modified dist shaft assembly would definitely be easier.
I spun the pump for about a minute (slowly at first) until it primed, and ran it for another 30 seconds or so (there was a surprising amount of resistance once the pump started moving oil).
The rear main seal went in easily, took my time and used quite a bit of liquid soap to lube the top half. Like I said the toughest part for me was getting that oil pan back in place and aligning the new pan gasket.
The old oil press was 40 psi at start up, dropped to 15 psi when warm at idle, now it's about 50 at start up and just below 40 at idle. I've only put 50 miles on it, but so far the new seal is dry.
I've never participated in a forum like this before, I'm looking forward to learning a lot.