Alright. I dug the tank out from behind my Mother's shed. She was happy to see it go, I'm sure.
This is the new tank. It's sitting on top of the 7 ton tank cage.
As you can see, I've been using it as a table for spray painting.
Here is the new 73 US gallon tank sitting next to the old 39 US gallon tank.
And here's the best part. You can see from this angle that the new tank - though almost twice the size of the old tank - will take up the same amount of space as the old tank+cage! The tank is actually an inch or two shorter than the cage, it's just the angle makes it look the opposite.
Looks like I'll have to relocate the fill spout on the new tank. I'm sure I'll re-use the old tank under the bus eventually, but the bigger tank is much better use of that undercarriage space.
Now, how do I mount it?
Here's an initial idea.
I'd like to be able to drop the tank without removing the brackets from the frame. That'd be nice.