The scale length (from nut to bridge) is different and unless it's specifically a conversion neck, the bridge placement is different. So you would have to nudge your bridge back maybe 3/4 inch for a Strat neck, compared to where it would sit for a 24" neck.
the butt of the neck is technically close enough. but like stated before, it won't play right.
a generic squier strat heel will be "CLOSE ENOUGH" for a mustang neck later on, but, there may be a 1/64th of an inch difference on either side. still won't be as bad as some cbs fender neck pockets.
