A Chevy parts guy informed me that a 69 rear end is wider than a 67, 68..

What are the facts as I'm about to install a 68 in my 69?

Same rear.
He could be confused with 70 and up ?

Should be 60 1/4" flange to flange.

Same width. Firebirds can be 1" wider.

Frank you have seen 69 Firebird with 61" rear?I thought they were the same as Camaro.

I had a 67 firebird rear and it was wider. I don't remember how much

Almost / Maybe all as I did not measure everyone I ever touched, the Firebirds I have seen are "Wide Track" longer rears.