I would say Small as the A12 cars were built a little earlier and they are small. This is my take from reading the A12 Liftoff Hood registry forum.
My car was built May 7th and it is a small font.
(I had to change my post because I keep getting my large and small font radiators mixed up.)
My A12 is a SMALL FONT radiator and my dad's 69 RR is a large font Oct built car.

As Mike said it Should be a Small font one in your car in my opinion also. Sorry for the mix up earlier.