Generally speaking, for a 1991 Camaro V8, a 10W-30 or 10W-40 oil would likely be appropriate. In hotter climates, the 10W-40 might be preferred, while 10W-30 might be suitable for cooler climates. Using a modern oil that meets or exceeds the specifications listed in your owner's manual is important. Look for oils that meet the API service classifications recommended in the manual (like SG, SH, SJ, or later).
Do not rely solely on this information. Consult your owner's manual for the correct oil grade and specifications. Using the wrong oil can damage your engine.