How interchangeable are 318 harmonic balancers?

I'd love to see some pictures of this car when you are done

presume its a 770 trim level car i.e 2 door hardtop 1968 dart body with the 1970s "European car" inspired grill ** and slightly compressed nose.
Dave,

Yes, it's a 770 Regal Hardtop (Mexicana, as well), and I posted a few pictures of it in my introduction thread:

https://www.forabodiesonly.com/mopar/threads/new-member-with-an-interesting-story.545325/
I have many, many more pictures of it, but I hesitate to post too many of them here since, A) I think people may get tired of seeing it/them, and B) it's not my car, and I don't know how much the owner wants me to "share" in public. (And sadly, I can't ask him right now, as he's back in the ICU as of Wednesday eve.)

But feel free to shoot me a message in the PM/Discussion area here, with your email, I'll be happy to discuss the vehicle with you "offline", as it were.

Jim