my dad has a 96 discovery with the 4.0 and the other day he was driving it to town and he got to the end of the road ~1/4 mi....and he noticed the oil light never came off. he tells me when it is running you can check the oil and the oil stays in the pan. im guessing the oil pump is out. we are going to change the pump today. can you get a pump from anywhere except the dealer? will the pan just come off without many problems? is it pretty straightforward? can you give me some tips on how to do this? any special tools? thanks

The pump is in the timing cover. You need to remove the fan, water pump and damper to get it off.

Before you replace the pump I think you should pull the pan and check the pickup tube. They have been known to clog or even come loose and/or fall off. All of those are fairly easy and cheap to fix compared to pulling the front cover and replacing the pump.

I think one should put a mechanical oil pressure gauge on the truck before anything else is done.

I find it doubtful that one can check the oil level with the engine running. The crankcase is a pretty violent place when an engine is running.