You had asked questions about the gear, on the rejected opinion. There doesn't seem to be any specs available on the sizes of the pinion gears nor a gear tooth count. There is two basic versions of this part, the original and the updated. Neither are all that heavy duty, it is a weak spot in the transmission. There is a heavy duty 5 pinion gear version available to upgrade with. It is specifically a rear 4 pinion reaction gear planetary assembly, for the 82-up th700r4 and 4l60e transmissions. Made by Gm / Ac Delco.

This is part of a reaction gear assembly, specifically the reaction carrier assembly. It installs into the ring gear portion of the reaction gear assembly. It works with the low and reverse clutch. Also known as rear planetary gear set. The number 10 and 078 don't seem to correspond with any part numbers, could be casting dates. The part looks identical to the same gear set in a gm th700r4 automatic transmission. Would have been manufactured by General Motors

References:

I have rebuilt several of these transmissions.

Reason:
Another opinion was accepted instead.

This is part of a reaction gear assembly, specifically the reaction carrier assembly. It installs into the ring gear portion of the reaction gear assembly. It works with the low and reverse clutch. Also known as rear planetary gear set. The number 10 and 078 don't seem to correspond with any part numbers, could be casting dates. The part looks identical to the same gear set in a gm th700r4 automatic transmission. Would have been manufactured by General Motors used throughout the production life of this transmission. Just about all gm rear drive light duty vehicles in the 80's and 90's

References:

I have rebuilt several of these transmissions.

Reason:
Hey, you are right that it is a planetary gear, possibly rear. I also thought it was for the GM tranny, but I posted on here because the planetary gears appear to be a different size/shape. Does that matter? Otherwise it looks the same, only slightly differnet size.

You had asked questions about the gear, on the rejected opinion. There doesn't seem to be any specs available on the sizes of the pinion gears nor a gear tooth count. There is two basic versions of this part, the original and the updated. Neither are all that heavy duty, it is a weak spot in the transmission. There is a heavy duty 5 pinion gear version available to upgrade with. It is specifically a rear 4 pinion reaction gear planetary assembly, for the 82-up th700r4 and 4l60e transmissions. Made by Gm / Ac Delco.

References:

http://m.ebay.com/itm/GM-CHEVY-700R4-4L60E-TRANSMISSION-REAR-PLANETARY-GEAR-4...