I've tried the whole 'red hot propane torch/wet towel thing' and wasn't that impressed... but it was on newer sheet metal and I was wondering if I might have had some alloy/hardening issues and other stuff affecting the results. I also tried a similiar setup that I believe was sold by matco or snapon as an addon to a mig welder that basically was a copper tip without the wire feed to do the same thing, create a red hot spot where you want it... again, it worked but I wasn't impressed.
As far as a shrinking disk, I made my own (had some scrap stainless sheet, taped a 7" cutting wheel on it and traced it with my plasma cutter, making a perfect disk with the hole in the right place. I sanded off any slag off the cut surfaces and then found a pot in the kitchen that was slightly smaller than the disk and had a piece of MDF that was slightly smaller then that, put the whole assembly on my press (pot, disk and then MDF) and pressed them together putting a crown in the disk/bending the edges back.
I have to say that works absolutely incredibly well for shrinking while making the most hideous screeching noise....