http://www.classicseacraft.com/broch...production.pdf
This is in the brochures section and gives the break down by year.
I bought a 1970 Seacraft a while back with a MA gunnel cap. It had a FLZ HIN, but I know the hull was built before 1972 b/c of the 4 stringer setup . . . Probably means that there are only 326 left.