Diff Ratio Dilema

Go with 3.91's and a 28 inch tall tire. Here's why.....the rfe545 has a 3.001 first gear, and outta the hole you move the car like a scalded cat on a hot tin roof, and with 4th and 5th being overdrive (5th is .67 is memory is correct) with a 28 inch tall tire and the 3.91's you'll be turning 2kish at 70mph. Now I'm going off memory when I did this swap in a 64 Polara 500 so I could be off a tad.