Opinion only dont'get jacked off
But prices of cars is really what the buyer wants to pay. Both Cameros and Mustangs can be valuable if you don't mind sitting on them a while. But remember this just because it is a Camero or a Mustang does not guarantee its value. The 67s were not most desireable. It appears to me its a very plain jane car that is not one of the valuable models. Remember the 67 was the beginning and it was really an economy special not a hot rod. Spending bucks on engines is fine if your buyer is into engines.
You need to contact a Camero expert...i.e. the guy in my neighborhood has several and knows their most valuable ones. In your area there has got to be one.
I would take off all the expensive engine and add ons, put in a clean 327 and paint it. Then you won't be insulted at the current offers and can either sell the engine sperately or build another car.
It really bothers me that so many people are led to believe just because its older or has Camera/Mustang or what ever its valuable you gotta know what is worth building before you build it.
prime example if this are the 55-56-57 Chevys people think they are valuable but only certain models like convertables and nomads are worth hauling home.
Think about what you would want. Look around some; asking prices are always just that asking. Perhaps your current offers are just right..I certainly would not pay much for a 67...but an item with hide away headlights, yenco flags, is worth looking at.