I have a 1977 SB with 130,000 miles.  I don't think the engine has ever been rebuilt but it runs well and is not a daily driver.  First time out this spring I checked everything out, oil water, air rubber ect., everything looked good so I hit the road.  After about 18 miles the oil pressure dropped to zero, fortunately I was in front of an Advance Auto store.  I pulled in, checked the oil and found I was 3 quarts low.  I added the oil, the pressure came back and I drove home.  The next week I took out the car again.  This time I drove about 40 miles and the oil pressure started to drop, when I got home I checked the oil and found I was again 1 quart low.  There is no smoke when the car is running only a small puff when I first start her up,  I would think with the amount of oil missing I would be smoking like Mt. St. Helena, but there is none.  Also the garage floor remains clean.

Any ideas where else I could look for the oil?

Ok... this is the THIRD time I've tried to post a response here!!!
That's a lot of erl to lose without the car smokin like a freight train!!
Look under the car, for oil on the underside of the body/chassis. If it's leakin while you're drivin, it will blow back onto the underside of the car.
Check your PCV valve, and see if it's gummy, or stuck. If it is, it will create a tremendous amount of internal pressure in the engine, and create a leak only while driving. Then the oil comes out of the valve covers, pan, or front/rear seal.
I did build an engine once,(many moons ago!) that would suck the pan dry in about 5 min. of running time! That turned out to be a crack in the block, by the oil galley, and the oil was being pumped into the radiator!!
(I doubt that this is your problem, but just felt the need to share!!!!)
Check under the car, and you'll probably find your missing oil!!
Adams' Apple38539.8432060185

Took a week to find the time but as suggested did the easiest first.  No oil on the engine or on the under carrage.  PVC valve looks new, I replaced it about 1,000 miles ago.  I only pulled the right side valve cover but everything looked OK.  I even checked for oil in the coolent, nothing.  Any other ideas out there I hate putting it in the shop but I might have to.

Only other place it could be goin' is out the tailpipe!