I wanted to try to tack all the pieces in a row to make them all the same. But, after looking at the setup I had and the potential problems for movement in the middle, I opted for a single jig. SInce the dimensions were all even, I was able to make a simple setup using a steel bar, a stack of washers 1/2in high and a 1in sqare piece of tubing. A couple of bolts and clamps later I was in business.
The result is all the tubes are in line with each other and the don't rock on a flat surface. Next is to finish welding them and then weld on the tabs where the brake cylinders attach.