Interesting Blog by guy that worked for CMC in the era. He says the 359 uses thicker fiberglass than 356 shells. Hence, heaviest shell CMC produced. Engine bay was made to fit larger, more powerful engine to compensate.
https://classickitcars.wordpress.com/about/
https://classickitcars.wordpress.com/
Check this CMC mod - bonding 356 body parts to a 911 to create a 959.
And a 959 Targa conversion.