[cobrajam]

The 6090 means it was cast as a cylinder head. I do not think there was much change among the C6AE-Rs, I think they were '66 352 heads. Several FE guys swear by them that they are the poor man's version of the 427 heads with close to the same ports and runners. They have 72-74 cc chambers. I would look at the dates to see if they were 'matching'. Should start with a 6, which would designate 1966. The second should be a letter, A=January, B=February, etc., and the next numbers would be the day of that month. If they fall within a week or so, I guess you could call them 'matching'.