I had a parts watch with a broken mainspring, I took, (very carefully) the balance wheel and the retention pin out of that movement and attempted to transplant them to the #24 movement from the Marlin. I almost made it, as I was working to get the hairspring through the hole in the adjustment lever I heard a nearly inaudible tink, I looked down to see the hairspring folded over on its-self. I straightened it out, but it's shot.
On top of that, the retention pins very easily become minute ballistic projectiles.
Anyone know of a source for replacement balances and pins?