Thank you, squeeze!
Exploding u-joints aside, that sounds perfect. I'm sure the panel's must have had rear leaf springs, not trailing arms, so if a GMC frame is the same as the panels and suburbans, that would be a great place for the tank.
Anybody know if a panel truck frame is the same as that used on the short-bed or long-bed 1/2-ton trucks? I guess it wouldn't be surprising if the panel frame was more similar to the 3/4-ton long-bed trucks.