I have a stuck heat riser on a 216. It is rusted in pretty good. I've soaked the shaft to manifold interface both inside and out with all sorts of stuff for almost a month now and no luck in getting it to move. I would like to remove the unit entirely and replace the shaft with a stainless steel piece and re-attach the weight and "butterfly" as well as machine the slot for the spring. I was wondering if any of you out there have done this "operation" before.

1951 Chevy 1/2-Ton 5-window