My '71 ain't a '71...or is it?

That sure looks like a 71 heater box set up in the pics.

A 73 heater box wouldn't bolt up without cutting and modification.

I would say it's more likely they shipped you the wrong gaskets.

I appreciate all the help. I will say that the kit they sent me says on it 67-72 (I misspoke and said 68 earlier), and the instructions have pictures of the heater box which is night and day different from mine. Hopefully your pictures will help explain better. Thanks again