That kit looks nice. Polyurethane bushings do tend to squeak though if you are anal about a super quiet ride. You can find front spindle kits to upgrade to 5-lug in the front online if you search around. To upgrade the rear axles to 5-lug, I'd probably just go ahead and throw a 9" rear under there to handle the power of the 351c. Depending on the overall width of the rearend, you could even upgrade to a 8.8 out of a newer Mustang or Explorer and get rear disc brakes. Depending on the size of your rims, you can even upgrade to 13" '03 Cobra brakes in the front from Mustang Steve: cobrabrakes
Also, if you want a little bit of a rake in the front, you can leave the 6-cylinder front springs in the car and the extra weight of the 8-cylinder motor will push it down a little bit.