Calibrating Speedometer 1988-1991 Chevy GMC - OBS Project

Finally fixing my speedometer!
A special thank you to SomeOtherGuy off the gmt400 forum for his work seen here:
www.gmt400.com...
His write-up helped me along and if you may decide you want to follow his example and add switches to make it more serviceable.
I also use the website below for calculating the tire sizes and differences:
tiresize.com/c...