Hi,
regarding the question about spare tire rims and sizes it is like this I think:
Version MY up to 1986 is: 165 - 15 4 PR 83 P and 5x15 rim (though Porsche did not document this very well)
Version 1986 up to 1992 is: 165 - 15 N 89 and 5,5x15 rim
Version 1992 up to1995 is: 165/70 16 92P and 5,5x16 rim (related to standard 17" rims)
