What do they mean

I have a 1966 Plymouth, Valiant that was a drag racing car, it had a 340 four speed in it for racing, I bought the car less engine & transmission, it has the following letters & numbers combination on all the windows ; SS / J with the number 326 under it, what do they stand for. ?

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It wasn't SS legal with a 340. I'd have to get out the rule book and see what J is but it's probably a 273.

Keep the stick.