Well, I went ahead and got the SA-200. The seller got it running and it started, ran and welded nicely. (He said the choke had stuck on it.) He kept the battery (after negotiations, don't know if that was original intention) and the exhaust stack was loose. I appreciated the machinist friend's offer to let me use his equipment, but prefer having it available whenever I need it without having to go get his.
The exhaust stack was welded to a 1 1/2" pipe coupling which was screwed onto a 1 1/2" x 4" pipe nipple. The nipple had been "brazed" to the exhaust manifold but it had come loose. There is no evidence, that I have seen, that the exhaust manifold was penetrated at all with the weld which seemed to just stick to the nipple.
Question: How is the best way to put this back onto the manifold? I considered: 1) TAP the manifold for 1 1/2" pipe and just screw it in.2) Design some kind of bracket for the nipple to screw into and then tap a couple of holes (? 3/8" or 1/2") into the manifold for this to bolt on. 3) Attempt a weld to the manifold, as was attempted before.
A diesel mechanic told me that I'd probably have to tap the manifold as not much would weld to it, as far as he knew.
One other alternative - a "press fit" - for the exhaust stack or the nipple to press into the manifold. Here I suspect I'd have to be careful about splitting the manifold if too much pressure is applied.
I'm open to other suggestions. There's no rush. It will be a spare time project. I currently have a Campbell's soup can sitting over the hole to keep water out of the engine.
I expect the diesel mechanic is correct, but wanted to check for all my options here.