Window sticker question

[Tarrytown SS427s]

On a 1968 Chevrolet window sticker, does anybody know how they specified the M20 transmission? I think it was "4-spd transmission", but I am unsure. Any help is appreciated!
Steve

[Z28DZ]

Would appear as:

5M20AJ 4-SPEED TRANSMISSION

ps - I've seen the AJ as AD also. Curious as to the difference?

[Tarrytown SS427s]

Thanks for your help. I've always wondered what those two letter codes meant. It seems like they were usually just random, perhaps an internal factory code
Steve

[TimG]

They're ECL codes, they note specific items for the factory to use in conjunction with a specific option. These codes could note a different speedometer gear to be used depending on the rear end. This is a good way to bust fake paperwork if you have an ECL code book. Often times the forgers don't use the proper ECL codes. They may use an ECL code for a small block on a big block car.

[Rainer]

The M20 info on my 68 Chevelle SS window sticker is somewhat different:

[Z28DZ]

And to correct myself, I was looking at a window sticker for a '69 Camaro. I am looking at a '68 Camaro window sticker from Jerry M's book and it shows it as 5M21BA - 4-SPD CL RATIO TRAN.

[TimG]

I believe that different assembly plants had different numbers/letters preceding the option. I'm most familiar with Corvette window stickers that were all from St. Louis. I've noticed different information in the body of LA vs. Norwood window stickers noting the assembly location. ECL codes are the same from what I've seen.