Don't be afraid to wind that 325 up a little more, the governors were set at 3800 rpm, so if you push it to about 3500 you'll be close to 60 mph. without doing anything to the drive line.
I run my Tow Truck with a 350 sbc (same rear and trans as you) up to about 65 mph on the interstate and still have pedal left. I don't have a tach, but guess I'm in the 35-3600 range (I have bigger rear tires, 10.00 x 22.5's).
Mike B
