I upgraded my suspension earlier this year with this kit:
http://www.p-s-t.com/gm/gmfdbkconv.html
Note - "will fit most 14X7" - didn't work for my original 14" Rally IIs so I had to upgrade to these:
http://store.summitracing.com/partde...5&autoview=sku
The colors are off a bit but I'll take care of this over the winter. I have the 245X60X15s and have not had any problems but then again, I do have new springs all around and the car is sitting higher than what it was prior to the upgrades. I've attached a few pictures for your reference - hope they help.