Will the 2010 Camaro steel wheels fit on a 1987 cutlass without spacers or adapters?
You need adapters. Three problems. The Camaro rims have a deeper backspacing, they use a 5x120 (vs 5x120.7mm or 4-3/4") bolt pattern, and finally, they are set up for a M14 x 1.5 lug nut. However, here are photos of the 2" wheel spacers specifically for fitting 5th gen Camaro wheels onto a G-body or S10 trucklet. I picked them up from Garage Racing on EBay, $150 for four. Auction #191084806577
Unlike my first try at adapters last year, these fit perfectly, no issues with the taper of the Malibu rotor hub. They sit flat and index on the lugs, just tighten in a star pattern. Haven't tried them on the road yet, but they look like they will fit the fenders even with the Hotchkis lowering spring kit. I will end up using the Camaro lug nuts, which art closed and cover the threads.
You will find the Camaro tires are taller than the G-body, so they may rub the front fenderwells. A 235/45/18, or 245/40/18 is closer to G-body size.