What should be done with the G20 after the mechanic says, "The left 2 pistons are starting to melt and right 2 pistons have coolant in them due to blown gaskets".

You don't state how many miles are on this vehicle. However, with it being an 84, and not exactly anything collectible, I wouldn't waste money on it with the motor blown. If it's in really nice rust-free condition you might be able to sell it as is, as a "mechanic special" in need of an engine, if it looks like a rust bucket, scrap it.

Thank you for your suggestions. Ironically, the entire vehicle had been updated, refurbished and the "body is in exceptional condition". Thus, I'm torn. How much is this vehicle worth now if selling as is? Place on Craig's list?

FYI: Currently has less than 55,000 miles on it. The original owner kept it in his garage for 20+ years. My father then brought it real cheap ... and then updated, refurbished and finally modernized it.