Do you think this exhaust valve is deforming?

[montmil]

I may try silver soldering them if the JB Weld doesn't seem like it will work.

Mike,  Encourage you to choose one or the other. If the JB Weld doesn't meet your specifications, it's going to be a booger bear cleaning up the tubes and rings so the Plan B silver solder will stick. The soldering technique will also be quicker and is also somewhat 'adjustable' later on, if required.

A small, butane-powered soldering torch is mighty handy to have and would be useful for other shop chores. Big Box home improvement stores will have them along with the 'hard' solder you'll use.

While the heads are off, position them with the head gasket surface facing up. Pour a little kerosene into the head's combustion chamber and watch for any seepage through the valve seat.

Tony has good ideas pretty frequently. However, I once tried using Wifey's kitchen oven to assist in dismantling a car's brake master cylinder. Wimmens can be very sensitive. All I heard, well, all that's shareable in mixed company, was Bad dog. No biscuit.

[nhmaf]

Thanks, Monte.   I've already got the propane torch and solder, but I gotta get a new container of flux.   I was just a bit worried that my heating of them might get things slightly out of alignment as I won't be able to quite get 360 degrees around the tubes with them in the cylinder.

I think JB would come off with some heat, but it wouldn't be a "clean" process.   I'll see how things go..

[montmil]

Mike, the old-style PR rings were sometimes brazed in position with a couple tack welds. Heat requirements for the solder should not create alignment issues.

[Barry]

I think if I had this problem and had the barrels off  I would machine up some simple collars with a grub screw. That way once assembled the stop rings could be tapped to the desired position and the grub screw tightened. Having stop rings that are effectively adjustable would save the worry of precise insertion depth on the tubes.