What would they be worth?

CFD244 said

My April built '71 has an engine cast date of 1970 and J heads. It's a numbers matching car.

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My '70 Swinger 340 also has the fender tag, and the complete build sheet I found under the rear seat. They are also date coded correct J heads. 915 heads, 2.02 intake/1.60 exhaust.