My 78 is also clean. In WI. Let that soak in.
It was a county detective car kept in the county garage. Then it went to auction and the guy used it for 30 years to pull his pop up camper to upper michigan. That's it. Tucked away outside of camping season in a dry shed. Quit running it about 8 years back because it was blowing blue smoke.
Guy bought it before I could, pulled the engine and transmission, swapped with his brother in law's rebuilt 318/727(cam, intake, etc) and I drove it home. He got the original big block, told me later he had it checked out, cracked head, needed bored 60 over. I did alright
But I have not seen another within 300 miles of me, even a rotten hulk for parts in the couple years since. Well, I can;t say that. One came up with busted glass and the rear springs holding the trunk open from a cow pasture about an hour away. Rat infested interior, broken out glass, still had the 400 big block in it, sunk about a foot in the dirt(yeah I bet it turned over lol).
But people should get past the whole 4 doors grew on trees thing. That was a lot of years ago, and no one cared to save them until about maybe ten years ago now.