GO GTXJohn !!!

BVoelzke said

I would think low compression 340 , a 318 four barrel wasn't available that year , in an A body anyhow

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Both theses cars are 71 High Compression (10.25) 340 with Thermoquads.
They are both carrying a lot of extra ballast to make these classes:
Demon was 3370 at this race
Duster was 3460.