David,
My log book shows a cabrio and the car is a 82SC Targa. The only important body to know the true car type is your insurance company.
The chassis number your car has is Porsche what was called an interim solution before changing over to the international standard so you cannot tell what body type it is. For your info below is the detail from a book called Porsche 911 Red Book.
91A0134182
91= 911 (turbos had 93)
A = 1980
0 = factory of manufacture
1 = 911 (turbo = 0)
3 = engine version (3 rest of world, 4 USA, 7 Turbo)
4182 individual build number. The book shows 4,831 cars built (europe and japan) US 4,272 and turbos 840 for this year.
6303946
the engine is a 930/09 188 hp @5,500 rpm 188 foot-pounds of torque @ 4,200 rpm compression ratio 8.6:1
The M option for Targa build was M446.
Rats (Bones' assistant)