You can get wheels from several places with the proper backspacing so that you don't need spacers.  I got a set of 17" C5 Z06 replicas from a company on ebay that have done well for about two years now. Most of the used C4 wheels weren't much cheaper than these were new. Consider the cost of the spacers while you're at it unless you just "have" to have GM wheels.

I have a used 87 that came with wheels off a later C4, like 91-93?, which are 17x9.5 (instead of the stock 16"s).  It did have 270/40 R17s, but, when I got new tires recently, I took the advice of the tire store and went to 245/45, which are a bit narrower, but are still plenty wide and have more room in the wheel wells.  I got 4 new ones from Tire Pros and bought Custom "Sport XT" models, out the door for $508.00.  Not the fancy race-soft tires, but I drive a lot and wanted a more durable horse-shoe for daily driving.  You can usually find wheels and often pretty good rubber from someone upgrading to custom set, on Craigslist or other community resale sites, for a few hundred dollars, so the switch may not be that difficult.  Good luck.

I just bought a set of chrome ZR1's, 9.5 X 17, for my 1990. Mounted and balanced for $800. just tell them what make and model they are for and they can order them in the correct offset. No washers needed.

I have a set of standard 91 Vette wheels, no rubber, and I believe they are 17x9.5. They are for sale but I can't get to them until the end of April. They are in very good condition and in storage in Michigan and I am in Florida for the winter enjoying my 91 Vette with chrome ZR1 wheels. I do not know if they will fit you 87 but it sounds like they will according to an early reply. If your interested you can call me at (989) 280-4591 or thru a reply on the registry if possible.