Jack J,
See that no one has chimed in on this thread, so for what it is worth ------------.
Check out the reloading manuals as per case size and providing the STW shared the same head size with the 7mag. should be little problem.
I just checked out my loading books, and they share the same size head -.532" -, while the 7mag is 2.500" long against the STW's 2.850".
Unless there is an issue at to the length of bullet and/or velocity in the faster STW, it should be a simple matter of dropping the STW chamber reamer into the 7mag chamber.
Just pay the money to have a qualified gunsmith do the work.
Keep em coming!
CDOC