Stock offset on the 18"x7.5" OEM rim is 35mm. If you go with an 8" rim, i would also stick with 35mm offset; with 8.5", then 31 to 35mm ought to work out well. Check with the experts at
http://www.tirerack.com - they have tried fitments and know their stuff!
To be honest, I also kinda agree that the 22" wheels really do not do the car justice - it takes away from the unique look of the car. But, to each their own, so you can do what you want, of course!
Some things to be concerned about. In larger tire sizes, the available tires are expensive. And, they may not have the correct load index for the weight of the car. You should make sure to get at least a 94 (preferably higher) load index tire. And, keep it at 36psi or higher pressures (monitor it often!).
Check out
http://www.tirerack.com for available tire options before you spring for the wheels!
Z