Looks like OP has a SWB I6, so 16" wheels should work fine.
SWB V8 and LWB models used the larger brakes as well IIRC, and are limited to 17" and larger wheels.
As for the OP's tire selection, I would highly suggest looking at different sizes instead of different wheels. Stepping down to the 255/55-18 that came standard on my Saab will leave you with many options and a reasonable price.
i too have the 18" option.
tires that came w/ it were 245-60-18
for winter tires i ran 245-65-17 on TB rims ( that was before the lift, spacers and bigger tires)
the 17's are only 0.03 smaller in OA Diam. than the 18's, so speedo is only off a fraction.
IIRC the max tire diam. you can run is 30.5". after that you need spacers on stock rims.