MoPar hemi & six packs etc. aside,
I will go with the 1978 Mercedes Benz 450SE 5.0 Litre 160mph+ prototype I bought from a North America MB executive in 1988.
The 5.0 was not released to the public until 1985.
This was the 3rd 5.0 ever made.
Gray market a given.
Rattled all the glass in the shop while idling & came alive after 100 mph.
Embarrassing Porsche’s on the blacktop with a four door really brought out the salt. 
Owning automotive business back in the day really paid off sometimes when a customer wanted to wholesale a car needing repairs.
I will post more about this rare bird later including VIN if allowed or at least the motor number with so many zeros followed by a three.null
My dad was a real barn finding sniper.
What barn find story do you have?
PS
Hope it’s ok to post this here.