Ok, first off........as I tell my wife "I'm slow, but I do eventually get there", bishopts knows what he's talking about
SS input shaft has 31 gear teeth, counter shaft has 36 teeth
ZL1/ZLE has 33 teeth, 41 teeth
putting the ZL1/ZLE 5th gear, 0.82 (27/41) in the SS will make an overall ratio of 0.76, not desirable
Tremec makes a 37/54 set that makes a ratio of 0.80, much better
So, the answer to my question(s):
the gears are different on the input shafts
the shafts are not interchangeable
the shafts may or may not have metallurgical differences
there is definitely a difference in the tooth count
good explainer on the ratios in the TR6060