Almost surely your tach is reading high
Almost surely you have a 4.22
Recommendations: First determine what you have :
Jack up just one rear wheel and rotate the wheel 2 full rotations. Make a chalk mark on the wheel and on the drive shaft. Best to start with the shaft mark at some easily identified position- like at 3 Oclock. When you have rotated the wheel 2 full turns, you will clearly see that the shaft rotated a little more or a little less than 4 full turns. Just be sure you note which way the shaft was turning so you'll be sure if it went PAST 4 turns or ended SHORT of 4 turns. It will be only about 1/4 turn past the starting point (if a 4.22) or just an 1/8 of a turn short of the starting point (if a 3.89).
Then measure your tire rolling circumference- use a chalk and a tape measure to measure the distance of 2 revolutions rolling down your driveway. Half that dimension is your rolling circumference-should be about 74 inches or so depending on tire size. Divide that into 5280 Ft /mile = about 880 tire revs per mile. Multiply that by the axle ratio e.g.(4.22 x 880 = 3714). so at 3714 engine RPM you should be moving 1 mile in 1 min , or 60 MPH. Take it on the highway with mileposts and run the car at some steady speed or RPM and adjust speed / RPM until you are clocking 1 mile per 60.0 seconds. At that speed, (one mile per 60 seconds) you are going 60 MPH and the RPM is actually 3714 (or whatever you calculated) regardless of what the speedo and tach say. Now you will know how far off your speedo and tach are.
In other words, once you calculate your Revs per mile, based on tire size and axle ratio, that number is also the actual RPM at an actual 60 MPH.
Or use the calculator Kevin has posted on his site:
http://mysite.verizon.net/vze3rjzs/images/tire-speed-calculator-v2.xls
Then you can swap in one or some of the following :
3.89 ring gear (from several sources new and used)
3.70 ring gear (from Rootes post vintage spares)
Rebuilt OD tranny from Jeff Howarth in the UK or ????
5 speed Toyota tranny - used
Repair and recal your tach
Good luck. Lots of people here have done the above swaps
Tom