Looking for gear details

This is probably a long shot but here it goes
The pinion gear on my front wheel final drive gear box let a couple of teeth go. I am looking for the correct replacement gear set. I have a B6001 4WD and so far the B6100DT parts book has been spot on for replacement parts. The problem is for the gear set there are two numbers with a serial number break. I don't know if that same number break applies to the B6001 nor what serial number break it would be. The parts in question are a 12 tooth pinion gear with part numbers 66711-56950 (older serial number) and 66704-56950 (newer serial number) and the 25 tooth bullgear with part numbers 66711-56960 (older serial number) and 66704-56960 (newer serial number). I don't know what the differences are in these parts, wider teeth? Different diameter? I was hoping someone might have a parts book that has the serial number break for the D6001 or some first hand knowledge of the differences between these gears as they are hard to find and apparently quite expensive. Thanks

Well, I hope this helps anyone else looking for front end bits for a B6001. It took some time but I did track down all of the required parts.
Turns out the B6001 I have uses B6000 front end parts as far as the wheel drop boxes.
Gears are hard to find but still available - 12 tooth pinion gear is 66591-56760 and the 25 tooth bullgear is 66591-56774. The 4 gears cost me a $1000.00, I almost choked. The tractor is running an pulling fine once again. These gear cases are running 75W-90 synthetic to protect those gears of gold. Word of warning, service this oil often, the repair is expensive!

Corrosion and severe wear on the teeth, they were worn to razors. Very much a lubrication thing. Just wanted to share in case I could spare somebody else the expense and time to repair.
You are right that the final failure was indeed a jerking when digging into a dirt pile. It was already far on it's way down the PF curve by that time however.

Thought I would update this thread in the event somebody runs into the same issue. Here are the repairs pics with part numbers for my B6001 including SKF bearings instead of Kubota.