If it is a plain RS (not RS/SS)the 350 is not original engine. im pretty sure the 350 was only available in a SS camaro in 68. There are a number of things you can look for to determine if the car is an SS. Multi leaf springs vs. mono, two fuel lines, front disc brakes (although some SS's did have drum front brakes), hood. Also get the VIN # and Trim Tag info off the firewall, and post them here or under Tag Team and someone can decode everything to figure out how the car left the factory. Also get the engine vin and code, these are located on a pad in front off the passenger side head, or possibbly down by oil filter if not original. Also does the car have any other options, AC, PS, PB, center console, gauges etc. Also what kind of transmission, auto or stick, Powerglide or TH350, 3sp or 4sp. These options help to get a better idea of what its worth. If it is plain RS with V8 i would guess it to be worth $9-11,000 depending on condition of body.
68 Ash gold RS 327