I didn't know it was legal to junk cars that people died in? Regardless, the 68 will not perform like a 92, I wouldn't buy a cheap *** rebuilt engine.
I would look around for a salvage yard with a cheap used 87-93 5.0 that has reasonable mileage. Should be able to pick it up for $450 or less.
Also, I'd try and figure out what is causing the ping before I jumped in and started swapping engines. What is the future of this car? Are you keeping it, selling it?
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