For me, it would depend on exactly which C & W he has and what I wanted to do with it. I love the looks of a Cleveland but I wouldn't want to deal with a 2V head version. If it was a 4V I would jump on it for $75. If you decide to buy the Cleveland, make sure that it really is a C and not an M. They look alot alike to the untrained eye. M's were never available in Mustangs, are taller, wider, and heavier than C's, and use different mounts and bellhousings. They are not bad engines for trucks and land barges but I personally think it's too much trouble to transplant one to a Mustang.
The W is much easier to find parts for and will fit better in early chassis.