Join us on Facebook: Search for 'ConcoursMustang' Private group!https://www.facebook.com/groups/concoursmustang/SAAC-50 , Sonoma, CA August 21-24, 2025http://www.saac.com/
Looks like it could be a julian date code. 31st day of 1966 second shift maybe?
Spacing seems to have changed on the ingots they used - apparently leading to the confusion. kcodecoupe if the pan is believed to be original how does the date on the pan compare to the rest of the engines part decoded as you have currently?