Technical 57-60 Borg Warner T10 4-Lug Reverse Idler Identification

In my collection of T10 parts, I'm trying to ID a strange "4-Lug" Reverse Idler Gear and related Thin Reverse Gear.

QUESTION: Is the 4-Lug Idler Gear and Reverse Gear I have actually from the 57-60 T10?

DISCUSSION:

The B-W catalog notes the 57-60 Reverse Idler Gears are "4-Lug"
Subsequent years had the "spline" variant.

The HP6 catalog also states the Reverse Gear is a T10-46A which is used in ALL T10 and Super T10 transmissions. Same goes for the Reverse Idler Shaft: ALL T10's.

So check out this picture: My 4-Lug Idlers have a narrower spur gear as well as one Reverse gear I have. All the others are later Spline Idlers which have a wider spur gear which all the other Reverse gears also have. It would seem that 57-60 had the Narrow Spur and the >60 have the Wide Spur.

But how is this possible if there is ONLY ONE Reverse Gear Part number???

Here is a pic comparing the differences in spur gear width:
Also note the Idlers have the same stack height and bore and the sliding Gear has the same spline

 

Most likely because the later wider reverse gear superseded the original narrow reverse gear - works fine with the original 4 lug idler ***y

 

Given the collapse of the T10 used parts market and while blown reverses are probably the most popular gear replacement, there is probably no reason whatsoever to put a 4-lug back in a transmission. Unless someone is OCD about maintaining the transmission "original." I don't even think the Pebble Beach Corvette Guys care either.

 

The well healed care when they shell out $$$ for a so-called "matching number" car.

 

You might have a point. Sellers may fully do***ent the rebuilding of all components.

 

Running production changes could account for the different thicknesses.