Is there anyway to determine my final drive and gear ratios when the tranny is mounted? Should I put the car on jackstands and turn the crank pulley with the car in 4th gear?

My tranny has a label on it that says S80. But looking at the Fatboy gear calculator, there are 3 S80 tranny configurations. I bought a JDM motor and tranny w/ LSD from HMotors. Does that mean I have the S80 with 4.4 FD and 3.23/1.9/1.36/1.034/0.787 gears?

 

You could do what you are describing to figure out the trans you have, but I think your guess is right, and you probably have the S80 out of the 93-01 JDM SiR.