Hi All:
Well, I always say you can drive the rig as fast as you are brave (or crazy) enough to do so!
Last Summer a couple of us Cruiserheads went on a day trip on the east side of the Cascades with a 4X4 club we had just met. On the way home, I was i nthe mood to get home, so going down the western side of Snoqualmie Pass (in a FJ40 with no top or doors) I must have been doing 75mph! The fastest I've EVER driven that truck; I've been accused of being a "Grandpa" driver!
If you don't have a tachometer, get one and install it on the rig. Most people don't realize that these old trucks are LOUD when one revs-up the tractor motor under the hood! Your "redline" with a 2F is about 4,000 RPM; I like to cruise at 2,100 to 2,500 RPM for best fuel mileage and quiet operation, but will definitely rev it up to 3,500 at times.
If your rig seems to be pooping-out around 60 mph the engine may have issues; need a tune-up, timing is off, carburator re-build is due, etc.
Regards,
Alan
Seattle