Actually, I have even larger wheels, Hydra, 6.5x16, with 205/55ZR16 tires, and no fitment problems at all. You'll find that 700 and 900 cars' wheels have a slightly greater offset, 25mm compared to the 240's 20mm, but that's only ~1/4 inch.

If you want to keep your speedometer/odometer accurate, you'll want to use 195/60-15 tires -- this size (called "plus one") is the size that was OEM with the 240's turbo option, including Virgo, 6.0x15, wheels, and is the exact same overall diameter as the na 240's 185/70-14 tires (the reason why the odometer and speedometer remains exact).

Of course, you can go to a wider and/or taller tire if you wish, but don't go overboard -- too wide a tire on a relatively narrow rim will diminish your handling because the "squeezing" of the sidewalls (to fit on the narrow rim) reduces the sidewall firmness that you would normally expect from a wide, low-profile tire -- in other words, it's a matter of diminishing returns; wide, lower profile tires are best fitted on wide rims.