Pull the speedo and look at the date on the back of it.

It may just be a Parts Dept replacement that was built with combination of parts. Or like was said a older refacing job.


Good discussion on 1968 150mph speedos:

https://www.forabodiesonly.com/mopar/threads/1968-150-mph-discussion.492704/

Nonetheless, some can just buy a screw in speedo cable and run it in a 69-71 car. Or just run it in a 67-68. The straight up numbers are easier to read.