Since the Big Boy transmissions are essentially two transmissions bolted together,
any two gear sets available can be combined to get the desired gear ratios. 
Subsequently, any addition in the way of more speeds would thus multiply accordingly again.
When looking at your B&J Big Boy, the unit closest to the engine would be considered the first gear.
The unit further away from the engine next would be considered the next gear and so on, and should be shifted this way.
What will fit in my car?
Here is a standard diagram of a B&J Big Boy in 2, 3, and four speeds with reverser.
Measuring a clutch pack during re-build.
Using a straight edge and dial caliper, measure from pressure plate to end plate. Then take the straight edge and dial caliper and measure from the case to the top friction in your clutch pack. The difference between the two is your clutch pack clearance. Good clearance is between .040" and .060".
If you need further information or technical assistance, please call us direct.
Big Boy installation instructions.
If you need these printed for your records, the images are provided in higher definition.
Please right click your mouse over the picture and save the picture to your computer, then print it for your own copy.
B&J Reverser instructions
Once again, right click and save image, then print for your records.
If you still have technical questions, please call for more info.