Is this stuff usable? Is there any market for it?

[gearhead_to_the_max]

I was given a bunch of scuba equipment by my father in law recently. It is all in excellent condition, but it's from the late 70's early 80's. I have;
1 double set- Aqualung/U.S. Divers Professional Aluminum Cylinder with manifold and ScubaPro backpack(yellow),
1 single- Aqualung/U.S. Divers Professional Aluminum Cylinder with ScubaPro backpack(yellow),
1 single- 50 cu. ft. with ScubaPro backpack(yellow),
2- ScubaPro steel tanks(unpainted) with ScubaPro backpacks,
2- Nemrod/Seamco pony tanks(orange),
1- octopus rig with 2 Swimaster MR12 regulators and a guage cluster that has a depth gauge/pressure guage/compass in it.
1- octopus rig with 1 Sherwood 2000 regulator, 1 ScubaPro regulator, & a pressure guage.
Various other equipment- flares,knife w/scabbard, depth gauge, some new valves that screw into the tank, a part that attaches to the manifold/valve on the tank, etc..

The VIP decals on the tanks are all from the late 70's- early 80's. These tanks have always been stored indoors (in his den in the house), and all were full of air until a few days ago. I emptied them to transport them(I didn't bleed the reserve air, so there is still some air in them). I know virtually nothing about scuba equipment, so any help/information would be greatly appreciated.

[Lemonade]

Carefully photograph every item and list them on eBay separately. At least some of the stuff will sell. Worst case scenario - you lose several dollars for insertion fees.