Porsche 928 has 65 rear 55 front offsets try to stay in that area to reduce trammeling or tracking front end which can be disturbing. also front fenders will crack if they come into contact with wheels (ask me how I know) The 944 wheels will work. Look at stamps by valve stem for offsets
I am using 18" Carrera Lights 10" 65 offset rears with 285/40/18
8" fronts with 50 offset 235/40/18 they will contact fenders under load
