question about ring and pinion

[nightmare]

i recently purchased a used ring and pinion. i was told that this was a stock 3.42 for a GM 12 bolt rear. although, i count the teeth on the ring, 34, and the pinion, 10, it calculates to a 3.40. does that sound right?

also, the numbers on the ring are in between the teeth, so some of them are cut off. here is what i can read:
9 10: GM 783 (with the spaces being where the empty part of the teeth are)

here are the numbers on the pinion:
339627
10 37 10 78

could someone help me out and let me know what i've purchased? thanks in advance