I may be in the same boat as you are, in terms of building a ML from scratch. I've considered this many times and I have come to the conclusion that I need more woodworking and fine machining skills to attempt it.I know enough to not even try. Not everyone has the gifts that are required to build a gun. I can shoot 'em and fix 'em but do not have the patience and skill needed for the wood working.
Kudos to those that can but this ole boy knows his boundary lines.