I have a plate that I am not using, but it doesnt have the 123 plate. The 69's with 3 speed auto used a plate that had D,S,L on it which is what I have on it. Here is a link to one http://www.classicindustries.com/product/1969/firebird/parts/f5691.html
I will email you a couple pics of plate if you would like, just PM me your email addy.