Identifying air seal ring

I have just purchased an air cleaner with a hood seal adaptor metal ring on ebay for a 1973 454 BB. Can anyone tell me how I can know if it is the correct one for a big block. I have never seen the sealing ring for a BB advertised for sale at any of the usual corvette part suppliers and I have never seen onein the flesh. I have been told that the BB ring is not round but offset, the one I have received is round, any help would be helpful.
Regards Allan



