Rear end gearing question

[billdozer]

I've got a '49 3100 with a 4 speed on the floor with torque tube and stock rear end mated to a strong-running 261. I don't pull many houses down, so the granny gear is essentially useless, and I top out at about 45mph. It'll go faster, but it's comfortable under 50 for sure. I'd like to get it to cruise around 60-65 in 4th. I know about the T-5 trans conversion, but would like to keep it sort of period-correct (despite the disc brakes up front) and just swap the rear end gears to something taller to get better top speed. Tires are about 28" tall. I don't pull anything with it, but do haul a motorcycle and other stuff in the bed so I don't want it to be a slug. I mostly drive it on the street but wouldn't mind hopping on the freeway once in a while. 45MPH here in So Cal is suicide, but I think I could survive around 60-65MPH.

Anyone done this? Care to share how it changed driveability? Anything to worry about with this, or any reason not to?

(I searched first and didn't really find what I was looking for. Thanks for any input!)