The longerons going to the tail are telescoped down in size. The rule is, you need to have a 30 degree angle cut into the receiving tube and at least 1 1/2 diameters worth of the smaller tube must be in the receiving tube. For example the large tube is 7/8"x.058 and a 3/4 tube goes inside it. The 3/4" tube must have at least 3 times 3/4" (2.25") completely inside the 7/8" tube. Below I am welding up the splices. I use the block of steel to hold it until I tack it, then just roll it as I weld.

Now, I set the spliced longerons into position and tack them to the forward fuselage.

The tail area is tacked into position. A block of wood with two holes drilled in it is used to hold the tubes in place. I drilled the block of wood such that I could use it to place a level on it and level everything up. Also shown is a simple way to use a carpenters square to square up and hold everything in position. From here, I simply add the cross tubes.

The tubes in the back are left long and will be trimmed later.