It's a biscuit motor mount K but with 73-76 kmember provisions? Like the top stamping is 68-72 but the bottom is 73-76?

I've seen one in a 72 abody in person. I was thinking it was a transitional thing. I've seen pics of one someone had loose too.

IIRC, some 69 Bbody Kmembers come out like this too with 69 tops and 70 bottoms.

Now I wonder if the one in that 68 you are working on is a factory replacement part. Some replacement parts have multi year feature so one part number can supercede two or more part numbers. BUT any original car with pass through 73-76 sway bar would have spool motor mounts.

I think the kmember got replaced at one and the doner was one of the rare 72 cars that had that transitional Kmember. Just my guess.