It will fit just like a 5.0, except the 351W is taller and WIDER than a 5.0.
302 - length 27-1/2 Inches, height 20-3/4 Inches, width18-3/4 Inches
351W - length 27-1/2 Inches, height 23-3/4 Inches, width 21 Inches
These dimensions are important in the confines of a RBV.
I put a 69 351W in my 66 F100 short stepside after the 289 HiPo lost a rod, there was a lot of difference, not only in size, but in power output.
If you don't already have the 351W, I would suggest you acquire a 5.0 HO from something like a 91-92 Lincoln, they supposedly have something over 300 hp. My 92 Lincoln Mark VII was the last year of the 5.0 HO in that vehicle line, and it is a real go getter, even in that 4400 pound car.
For further information on this and other swaps go here and check out the "tech library" and while you are there register: The Ranger Station - Your Ultimate Ranger Resource