We have a 1987 Vette Convertible.  Looking to install new wheels (replica vette 18x8.5 front, 19x10 rear. tire size works out to be P255/40R18 frt and P255/35R19 rear.  Looking for comments and suggestions on tire sizes for the wheels selected.  Thanks.  I have a bunch more questions for later

According to TireRack the stock rim diameter for your car is 16 inches (didn't specify width).  The biggest thing to consider in going to larger and wider rims is the offset.  You may not have clearance issues with the rear rims/tires but you might with the front rims/tires.  Specifically with rubbing on the fenders and/or inner fender wells or frame when turning at full lock.