AD stands for Advance Design?!?! What is so advanced compared to non-AD? Forgive me, I'm new to this.

Thanks,
Tom


1951 Chev.P.U. Streetrod-project
1951 Chev cpe 261 5-speed-50%
1953 Chev cpe 350/700-95%
1962 Chev Bubbletop 409 -75%