You mean tow something like this

With one of these
Is this right, 1,500 miles a 4BT, the lead truck is a big sail with not a whole lot of weight over the rear, and the following truck weighs as much or more than the lead truck?
I would say about a 7.5 on the crazy meter. Probably can be done, won't be much fun, and could be a disaster.
I towed the above truck 3,000 miles in less than 4 days, coast to coast. the COE weighed about 7,000 lb, and my lead truck weighed 10,000 empty, then I had 3,000lb in the bed for most of the trip, but not the last 400 miles or so. The last part was not much fun, I often got the feeling that the COE wanted to pass me, particularly after a big bump on the highway, only way to straighten things out was throw the fuel to it and yank it straight for a few seconds. I had a 6V53 Detroit with twin turbos, about 300HP, that worked to smooth things, you may not be so lucky with only a 4BT.
I don't think your bread van will weigh enough in relation to the towed truck, and both having lots of area for wind to catch could be bad. If the tail starts to wag the dog you can only hope it stops, as you don't have a way to work the brakes on the towed truck, and not enough power to drive out of it. If it were only a short trip I would try it, but 1,500 miles is a long way to flat tow a combination like that.
Grigg