While my car is up on jack stands I plan on draining the oil and changing the oil filter. I will not be able to refill the oil for a couple of days. Is it possible that having no oil in the oil pan will result in the oil pump losing its prime?

IMHO, a few days/months should not be a problem. priming is a good idea if it has been sitting not running or empty for months/years. or installing a new pump out of the box.

I worry more about lifter bleed down when they sit for extended time (months/yrs) pump always pumps oil on start up but lifters clatter till they get pump back up and full of oil.

if you have a mech oil gauge you will see it fire off and a couple seconds later you see the psi shoot up. that's the time it takes for oil to go thru pick up tube/pump/filter/passage to sender port. then on too lifter galleys.

stock electric oil gauge may be a little slow to react and only seem to take longer. this is why I prefer a mech gauge. reacts faster on start up. if there is no oil flow you see it right away.

My car, a '70 340 'Cuda has only been sitting about a week since it last ran. I'm replacing the exhaust system and I thought since the head pipes were removed it would be easier/cleaner to change the oil and oil filter now. However, my oil, which I had to "mail order", won't be here until tomorrow. Once received I can add the 5 quarts but won't be able to start it for a couple more days when the exhaust system is completed. I guess my real question is: Is there any difference, where the prime in the oil pump is concerned, whether the car is sitting for a week with oil in the oil pan or no oil in the oil pan? Would simply draining the oil from the oil pan cause the pump to lose its prime? Thanks

It shouldn't be an issue.

filling the filter before installation will allow quicker pressure upon start up.

I would think that removing the filter would cause the pump to lose prime more so than draining the oil. Think thumb over straw.

I agree with this. I often let my engine sit over night and change oil before start up the next morning. this lets all the oil drain down out of engine and I don't have any oil spillage when removing the filter. less mess. keeps oil off me & the headers.

I have only had issues on BB engines not wanting to prime after oil change and had to back the oil filter off and let it purge the air pocket then it would pump/fill filter. but never on a SB engine.

When pan is full of oil, the pump is almost if not submerged in the oil. Not like a 440 where it hangs out on the front side of block.