The airgun store I make targets for asked me to come up with a 6 tank holder for their van. Everything I could think of seemed too labor intensive to bother with. So I thought this scuba tank holder would be the easy button.
When it was delivered it was too high and the holes were too large of a diameter, shit. Got looking at it and came up with this solution. Turned some foam pipe insulation inside out to make the upper holes smaller and it was a perfect cushioned fit. To raise the bottles I used round sprinkler valve boxes cut down about 4 inches. The curved bottom of the air tank fits into it well and puts the tank height at the desirable height.
Looks like you could make two racks out of one. Just screw some plywood to the flange and add the pipe insulation.
I'm afraid it would be too shallow if I'm thinking what you are thinking. When I took it to the shop they then told me they also use 45 minute bottles. Grrrrrr. So I took it home and put uncut sprinkler boxes on one side. The 45's would drop through or get stuck on the shortened side. The 60 minute still will work on the 45 side, just stick up a little higher.