Let me try it this way. All math will be 1(one) engine revolution. Engine pulley is 8" Transmission is 5"
1 engine revolution will equal 1.6 revolutions on the input shaft of the tranny.
Using the 350/400 gearbox here. The input shaft has a 13 tooth pinion gear into a 33 tooth bevel gear.
So the 13 tooth turns 1.6 times but only turns the 33 tooth .630303 times (13/33)X1.6=.630303
Now the 33 bevel gear is on the same shaft as the 25 tooth part of 3rd gear so the 25 portion of third gear turns .630303 times per 1 engine revolution.
The output shaft of the tranny is a 30 tooth driven by the 25 tooth that has just turned over .630303 times.
The 30 tooth turns .525252 times (25/30)x.630303 per 1 engine revolution.
So the output shaft of the 350/400 transmission in 3rd gear turns .525252 times per 1 engine revolution.
Using a 14 tooth sprocket on the tranny to a 44 on the axle.
The 14 tooth just turned .525252 times but only turned the 44 .167126 (14/44)x.525252=.167126
So one(1) engine revolution turns the axle .167126
Using a 49" roll out on the tire & cranking 7,000 RPMs
7000x.167126=1169.882 tire rotations per minute
1169.882x49= 57,324.22 inches traveled per mintue
57324.22/12= 4777 feet traveled per minute
4777x60= 286,620 feet per hour
286,620/5280(feet in a mile)= 54.28 MPH in 3rd gear turning 7,000 RPM
At the end of the day and having to take my shoes off to count my toes and even having to count some of my wife's toes this is what i come up with in order for you to run 60+ in second gear.
Engine RPM's = 7,000
Engine Pulley = 8"
Transmission Pulley = 5"
Second Gear = 21/34
Transmission Sprocket = 26
Axle Sprocket = 44
Tire Roll Out = 41"
MPH = 62.5