Hi Mel,
What I'll suggest is a lot of work to do. It may save you a bigger bunch of headaches later
The place my tires rubbed first were the backs of the seat buckets. I have the 17" wheels with 315-35/17 tires so their profile is a bit more square than yours.
Get the car on a lift. Start measuring distances to the nearest bodywork. Odds are, it will be the bulge in the seatback which will contact the innermost edge of the tire's tread.
Here's the sure way to do the next step - also the most work: Remove the shocks on one side - maybe only the lower ends of the passenger side shocks would do - and let the car down as far as the shocks can compress (you do have this minimum dimension in your notes, don't you?
). You'll directly see what will hit first, and when.
If nothing hits, you're in business and can measure the minimum clearance.
Then you can calculate how far you can move the tire inward and still remain clear of contact at full spring compression.
Sorry, don't know of an easier way to do this!
The alternate way is also work: get a wheel/tire assembly of the dimension you think will fit, install it and compress the suspension. Check clearance.
My E-M is a 2001 version. If yours is much older it may be shaped differently underneath, so take the seat bucket first contact point guess as just that!
Hope this helps!
Tom