Factory Manual Overdrive Transmission - What can you tell me about it?

[70chevroletCST]

Hey you! Yeah, you! I'm talking to the 67-72 Chevy expert. I've just discovered an interesting option that I'd never heard about. Factory manual 3-speed with Overdrive. Option M10. I did search for old posts but only found a little information. So really what I'm looking for is just whatever you can tell about it. How many years it was offered? What engines could be combined with it? How many trucks were produced with it?? Anything else?

This truck came across Facebook Marketplace a couple days, lasting only 4 hours before sold.. If only I had caught it sooner. I would've LOVED to have it. The best deals always go fast. Take a close look at that SPID. My interest wasn't contained to just the overdrive. Factory tachometer, paint stripe instead of upper trim, and positraction rear end. Certainly looks to have been special ordered rather than a standard dealership lot model.

Thanks in advance to anyone who replies!
Thanks to the Admins for keeping this great forum site alive!

1969 Chevrolet CST/10 Short bed