The motor itself will fit just fine. He'll need to use the Mustang II motor mounts and exhaust, which he probably already has. He'll also need to wire the computer up, but it's been done many times.
The flexplate for a Mustang II is 28 oz., and has to be rebalanced for 50 oz.
i just went thru this last year. any competent machine shop can do it for about 50 bucks.