The 351w block will fit with stock shock towers, but it is tight. I just put one in on my car. With an MII set-up itll have tons of room. There are notched tower options as well but they are rarer.
With a drag racing set-up I don't think the MII set-up would be a disadvantage, but I'm not sure.
1968 Mustang coupe 5.0/T5
Current Project: 1968 fastback 351w