Won't necessarily change your ratio, the big factor is tire height. This can vary quite a bit between mfg's for the same size tire.
Depending on how much clearance you need, shaving the wheel face would be the fastest route (the hub face can also be shaved a little).
Rims with a little more backspacing would be ideal (if available). The wire spoke rims are actually the correct rims for the slabside I believe.
These are the FIA (289) and 427 rims...
http://www.trigowheels.com/original.html
Not sure who sells the wire rims, but I think they're still available.