I just measured my 24" scale Mustang and my 25.5" scale Telecaster, and it seems to me you could just put a Strat/Tele neck on a Mustang body? The bridge will move about an inch back from the conventional Mustang placement, so you'd have to go for a hardtail bridge only and do your own drilling. A consequence would be that the bridge pickup would be a good bit further away from the bridge than normal. Also, the fingerboard overhang on the longer 22-fret neck is going to nudge really close to your neck pickup, depending on what route you choose (though there's extra wood on that overhang that could be easily trimmed back). Before you mail them $400, ask somebody at Warmoth to just pick up a Strat neck, stick it in a Mustang body and see what happens.... unless the rounding of the pocket is different or something, I can't see why it wouldn't fly. It might be neck-heavy, but that's a trivial issue IMO.