Anyone Seen These

Someone told me 273 and Hemi engines but not sure what years. My brother and I manufacture parts so we had them made which I should have by the end of the week. I have 10,000 coming.

But I am trying to narrow what specific years and engine range it covers?

They are sure cool looking. I have owned a lot of Mopars and have never seen them. Most likely they broke and were tossed in the trash many years before I got the cars.