Now understanding the goal I would question why one would even consider removing the HT with heat instead of just replacing with a new length. HTs are among the cheapest of frame tubes and I'll use generic USA 4130 sometimes anyway. But if you wish to try and learn I see no problem with that, being a learning moment.

When I saw the plans you have I got a chuckle in that you must have been wondering why we were referencing things like retaining BB height or steering angle You're pretty much on your own as to the geometry on this project. Andy