will a 351 fit in a Mustang II

Sorry, 351W has a taller deck. So the intake is wider and the block is taller than a 351C. The 351C exhaust ports down rather than the 351W which points out like the 302/289. So - really- the 351C should be an easier fit. A 351M is as big as a 460, so forget that unless you're taking a torch to the car. it's a damn sight easer to get headers on and off a 351C in my car than a 351W.
[addsig]