After obtaining a pan and stripping it down in preparation for shortening, the first thing is to measure the clutch and accelerator tube protrusion and exit angles from the floor pan for later reference.
Then unpick (angle grinder/hacksaw blade) the welds securing the clutch, accelerator, and the hand brake tubes to the chassis.
Mark out the section to be removed, Then cut and remove the excess section, an angle grinder is good for this task. Be sure not to cut the clutch, accelerator, hand brake and fuel tubes. Cutting the heater tubes will be ok.
Check that the hand brake tubes are welded securely to the bracket at the rear of the lever, and that the clutch tube is secure to the side of the tunnel. Re-weld if necessary. It may be necessary to add a support/brace, in the tunnel, for the clutch tube.
Gently guide the two halves together, guiding the tubes out of the back half of the pan and frame horns.
If the heaters are not to be retained, remove the heater cable tubes and weld the tube holes in the horns to prevent water entering the tunnel during creek crossings.
After a trial fit, measure for squareness, check level, and weld the two halves (Mig is best for this task).
Position and re-weld the clutch, accelerator and hand brake tubes in back half, cut excess tubes.
To shorten the hand brake cable, Take to your local brake specialist or boat rigging shop with length required. Or cut to correct length at handbrake lever end. Make a new fitting out of 10mm hexagonal rod, 70mm long. Thread one end 40mm (6 x1mm) drill a hole (just large enough to accept the handbrake cable) in the centre of the hexagonal rod at other end. Drill and tap one or two holes into the side to accept a setscrew. This will prevent the cable from coming out.
Before shortening the chassis, you may wish to remove both left and right-hand floor pan sections. This is done by drilling out the spot welds. Suggest you purchase a spot weld drill from a good tool supply shop, a 3/8 drill will do the job.
With the left and right pan section removed, shorten and re-weld the chassis. Then shorten the new floor pan sections and fit. It is easier to do it this way but involves a lot more work. Instead of refitting the pan section you may wish to use 2mm sheeting.
To add strength to the sides of your body you may wish to use some thick wall 30 x30 mm RHS, either inside or underneath. Bend to required shape (cut out a v and re-weld or have it bent at fabrication shop) put a length of 20 x 10 mm flat inside the RHS, secure by drilling some holes in the RHS, then spot weld (through the holes) into position, cap both ends. Mark holes in RHS to coincide with mounting holes in floor pan/body, drill and tap. Apply some rust preventive into the RHS through the holes, done this way no water will enter the RHS and should last many years.
During the pan shortening you will have noticed VW used a sealer in some of the joins, remove all remaining sealer and clean, reapply new seam sealer.