Since this post began, I installed a Gear Vendors O.D. to the back of my SM420. I can now travel 80 mph in 4th over at the same rpm as 60 in 4th. The split between 3rd and 4th is pretty cool as well. Just what that tranny needed. Anyway, I'm tickled pink about it. I'm also broke. I did the O.D. first, drove it a while, and then switched to radials. That also made a HUGE difference in how the truck rides and handles. Then a little dynomat in the cab, new shocks and now my truck rides like a modern truck on the freeway.
I also found out since then that a Columbia O.D. is basically a 2 speed rear for the old Fords. My neighbor is rebuilding 2 right now.
