A stick is what you need!
Decide how much you want to shorten her by and then cut a stick to the same length. As long as you cut every panel to the length of the stick, you can't go wrong!! Well, it worked for me!
couple of suggestions:
Obvious, but strengthen the chassis with plenty of plating once you welded it, especially if you're planning on doing any recovery with a kenetic rope!
Get a cutom tank made - I had one that followed the slope of the rear seat and to the full available width and held about 18 gallons. Made a filler pipe and cap that exited thru the rear three quarter panel.
Roof is hardest as it curves. Find the straighest point and either get someone who can weld ali to do it, or pot rivet it to an overlapping plate, which it what I did. After that I glued aircraft carpet to the roof to keep the noise down.
Sometimes the rear tailgate frame can be in a bit of a mess - worth doing plenty of work on this or get a better one.
it's a lot more work than it looks tho, so allow plenty of time!
If you need more pix, I can probaly dig some out (72 - 2 door model)
Good luck