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.
Check this CMC mod - bonding 356 body parts to a 911 to create a 959.
And a 959 Targa conversion.
Trio of cars (Targa, Cab, and Coup) built on Real Porsche’s built at Classic Motor Carriages in the late 1980’s.
They were called the “Ultima” and for a modest amount your Porsche 911 could be fitted with a fiberglass body kit that would make it look like a real Porsche 959.