A '79 Mustang is a whole 'nother animal compared to a '78.
Sure, the quasi-MII stuff is pretty good, but why spend a truckload of money to end up no better off than you were? If you were starting with, say, a knuckle-joint '39 Chevy with no useable parts, the MII might be the way to go.
I have a few old Chev's, a '52 and a '54, and there is nothing wrong with the way they work. I have also had to drag some Mustang II's off the road after they tripped over their own front wheels for no apparent reason. One went end over end on a straight road when a cross wind unloaded one front wheel. No thank you!