"but russ," I can somewhat implausibly hear you saying, "how do you make the frame ends come together? you dont have any wheels on the stanchions"
well, you add temporary wheels! I used two jacks, only raising it just barely enough to let the rear wheels roll the rear section into the front. the second jack on the front is just so the slightly raised rear section doesnt bang into the lower front section.
after that it was measuring and more measuring. I did two difference reference points on the front to two different points on the back, as well as a cross measurement from the oval hole on the front to the opposite rear cab mount to check for square. everything lined up perfect, with only a small whack or two needed.
tack weld, measure again, and weld solid.
a couple points to make here:
1) the overlapping section of the front half usually has a "bumped out" section on the rear half inside reinforcement, but you cut that bump off, so I like to tack weld the outside and tops, then use a c clamp to squeeze that overlap back to the inside boxing.
2) your inside boxing will need to be cleaned off at least 1" on the inside of the rear section before sliding it together, or it will stop before bottoming out.
3) there are two points, one on top and one on bottom, where the inside overlap will be full of weld over the front frame underlap, you will have to clean this out with a cutoff wheel so the frame sections can slide all the way together. alternatively you could just trim the rear half so it will still go together, but it doesnt take but a second or two to just chop it clear.
here is a picture, the red line represents where the underlap of the front frame section is under the rear frame section, and the red rectangle is where youu need to open it up, top and bottom, on both sides of the frame.
hopefully this helps someone.
tomorrow I am busy but I might get the new motor mounts and trans mount welded in and the frame powerwashed.