I remember reading a comment that someone made about the kits based on different tooling. The '71-'73 Impala/Caprice versus '74-'76 Caprice. This would make sense since the '74 Caprice had so many changes, including the greenhouse, it would make sense just to tool up an all new bodyfor '74. Since I have looked at a few promos/kits of the '71 though '76 (Impala/Caprice) over the years, it does appear that the '71-'73 body is totally than the '74-'76 version.
If this is the case, then maybe the '73 Caprice body tool insert exists somewhere in the archives at Round 2. If possible, they could reissue it again along with the '76 Caprice interior/chassis to make a complete kit out of it. It wouldn't matter to me if the interior and chassis was slightly incorrect for that model year. We have enjoyed other (thought to be long lost kits) that are like that.
If anyone is questioning the "business case" for an endeavor like this, I'd say it would be a win/win for Round 2. You could do a custom lowrider/donk version and the police car version. The last version of this kit was the Canadian mounty police car molded in blue. I think they were only sold in Canada AFAIK. I say this because that version had holes molded into the roof for the lightbar. The prepainted "annual" gold version did not have these holes so that version was probably produced first.