Jones,
I guess the big question is what are you willing to pay. In my search for just ONE extra fuel tank, it has been an expensive proposition. And I have NOT been successful yet.
I figure about $300 for the complete set up. PER TANK. Then if they would swap you your 70 gallon ones... you might bring that down by as much as $100 per. BUT it depends on who you are working with.
PLUS realize that unless the tank has been steam cleaned inside, you WILL pay for haz mat charges. Not too bad, but still there.
Let me know how it turns out. Oh, and those 70 gallon ones? Why aren't you going to use them? Are they diesel or gas?
I've got TWO in tank pumps, but not sure if they work or not. Supposedly they do, but I have not tested them. If you want them, let me know. But they are JUST the pumps, not the whole assembly.
jim