Welcome to the club. It will look great and be a good looking
runner when you are done. It is good news about the heating
element - fingers crossed. Mine took a bit of work too and is
a keeper.
I took a look on the web for how to dissolve epoxy and a whole
bunch of not-to-tricky methods were displayed. I wouldn't be
surprised if the epoxy could be pried, carefully and avoiding
any marks, away from the boiler, hopefully allowing you to
unscrew the S/V. Have you tested the engine on compressed air?
God Luck,
Wayne