Hi Josh, AC is indeed the makers mark for Arrieta.

Here's a link on the year of proof code (date made):

http://personales.jet.es/rafa/b_punzones_eibar_fecha.html

Looks to be about 1986 (E2) or 1987 (F2)

All the best!!

Greg


Gregory J. Westberg
MSG, USA
Ret