[YTNUKLR]

Casting numbers on heads are usually different from part numbers, in my experience.

Real-world differences in SC heads: 78-79 USA had 39/37mm ports, 80-83 USA had 34/36mm. Euro engines kept the larger ports. That's it.

PS. I have a set of '81 heads I would be interested in trading for "big port" heads, + cash.