Swapping in a 351w isn't all that hard, if you use the factory exhaust manifolds. The two different headers available for the swap involve some work. I think (not 100% sure) that the Hedman's require the motor to be repositioned by using a plate. Another brand requires a battery relocation and some modification to the fender wells.
Also, depending on the intake/carb setup you go with, cutting the hood for clearance may be needed. If you go with a low rise intake, you can manage it without cutting.
Other than that, it's a drop in and go. No changes needed to fit the radiator, shroud, starter, etc. I did buy a bracket to adapt the 302 power steering bracket to the 351, but only because I wanted something that looked better than the hacked piece that was in there.
Good luck.