My 64 with a SB 350 a SM420 a two speed rear and 10.00 22.5 tires will run 55 the RPM is a little higher than I would like, but I can still make short burst to 60 it is screaming as high as I will go at 60, it’s a good runner but the motor is still worn out.
I hope this helps. Are you sure you are getting all the RPM out of your motor if you are in high fourth it should certainly go faster than thirty five. Are you sure you are not going faster and the speedometer hasn’t shifted to read in high? Somewhere in the speedo cable there is a little two speed transmission that shifts to read the different gearing in the rear end check to see that it is working.
