"To replace the shaft, you will need to do a lot of stud and bolt breaking to get to the flapper."
Good morning Carl. Although I did that job about 35 years ago I don't recall having any problems or breaking anything. Simply removing the manifolds as a unit then loosening the nuts on the 4 studs that hold the manifolds together gave access to the heat riser plate.
"Then you will need to separate the flapper from the shaft."
I'm not certain after all this time but I recall the "flapper" being riveted to the shaft on my '36 pickup.
"Then you will need to weld the steel flapper back on to the stainless steel shaft. This will require a TIG welder for an easy to do good weld."
When I did mine I had only an AC "buzz box" welder. That welds stainless no sweat using 316 stainless electrodes. I now have a tig and have that option also.
As Achipmunk points out doing it once and doing it right is a concept with merit.
