I have a 1971 6 pack Challenger that's missing the K frame. The build sheet calls for "74" K frame and not a "77" from 1970

I can't find a "74" K frame so I was going to try and make one. (A lot of 6 pack K frames don't have the coin to be able to identify)

Any ideas where I can find one or do you know the differences between the two?