Well I found so information that answers my question about length.

They aparently came in three lengths, with the early ones bieng short and the last one the longest by 6". All the back half of the cases are interchangable so if you wanted to you could shorten the box, by swapping the case around.

The belhousings bolt on differently but there is nothing about the two split parts of the centre case.

But I still dont know if they are any different in diameter, or if it is the tunel in the sedan bieng smaller than the coupe.