Hi, I am trying to find out when ford changed stud sizes on the 300 I-6. My 77 came with self locking nuts. I need a valve job and I picked up another head which has smaller non-locking nuts and jam nuts. I can't make out the code on the head and am trying to figure out when they changed so I know the year of the head. They both have adjustable rockers and hopefully will interchange. Thanks in advance.

 

According to the Ford parts catalog 73-77 used studs with 3/8"-24 thread. In '78 they switched to the smaller 5/16"-24 thread.

 

Thanks for the quick response. That helps alot.

 

Are the pushrods the same?

 

Yup, the catalog shows same pushrods 73-79