Restoring the frame was actually easier than expected. Once the body and frame were separated, the frame was stripped of anything bolted on. That included all the suspension, fuel and brake lines, and exhaust.
At first I thought I could do a good job of rust removal myself using a a small sandblaster and 3M rust wheel in an electric drill. After spending hours, with little to show, it was decided to have it professionally sandblasted. First all the welding such as new trailing arm sections was done. A considerable amount of time was spent locating the new frame members in exactly the same place as the old units. Layout was done by creating parallel lines far enough away from the sections to be removed so as not to be disturbed during cutting or welding. The two new sections were MIG welded back in place.
Before sending to the sandblaster, all studs and rusted bolts were removed and the threads chased. Scrap bolts were used to protect the threads during sandblasting. New blind nuts as required were welded in at the same time. It's amazing just how many bolts are used to mount the body, somewhere around 45 counting the bolts holding various extensions.
The sandblasting company specializes in blasting and coating structural steel for things like bridges. They sandblasted every inch of the TR6 frame to bare metal, primed it and put on two heavy top coats of some sort of black industrial coating. I think the cost was $190. There's not much that can be done about the inside of the frame. I used compressed air to blow out the road dirt and the considerable amount of black beauty sandblast grit. In the left rear frame horn was a pretty large mouse nest that had to be fished out with a wire. Before the car is returned to the road, I hope to give it a squirt of waxoyl inside the box frame. New brake lines and fuel lines were run.