We have two at the guide company I used to work at.
Can't remember the models, but one was an 84ish, would do about 60-65, might of had a little more in her, but that's as fast I wanted to take her. The other was a late 60's that they got at the end of my time there, never had a chance to drive her.
They really are like driving a big tractor, 4 speed manual with a two speed rear, with a F-N-R selector, so you had 8 forward and reverse gears. In a previous life, ours had a crane mounted on the rear, so it had full hydraulic take offs, and controls in the cab. Front and rear PTO's along with a hand throttle that we'd use as "cruise control"
It was a novelty to drive, because it was so damn big, but after 3 hours on a tour you were hot, sweaty, dusty and ready to get out.