I would sooner use an angle grinder with a cutoff wheel before a torch. Too much collateral damage with a torch and no way to get a nice, clean, straight cut that you could weld a new dash up to out of a donor. You'd still have to grind the weld bead down flush with the same angle grinder and a grinding disk, and then skim-coat it with bondo and repaint. If you do well, you should not be able to tell it was ever replaced.
If there are spot welds you could drill out, that would be even better. A lot less bodywork!
If you do replace the dash, one tip I've got would be to put the gauges in the dash if possible before you install the new dash. It is a real difficult job to remove/install gauges with the dash in place. I've done it, but wasn't fun.
But did you know that there's a company now that builds new 5-window cabs with new doors out of brand new sheetmetal for about 9 grand now?
Also, where I live in Taos, NM, the AD trucks are EXTREMELY common, and you see them all over the place just sitting in fields! Many of them are restorable. So not a bad idea to plan a trip out and take a look around.
