Head differences

[Orionsax7]

I was just wondering what the differences are between the mid-70s 318 heads?

2843675 318 1968-74 1.78 1.50
3769973 318 1975-83 1.78 1.50

What's the difference?

-Alex

 

[Mrmopartech]

The heads are basiclly the same,the 9973 is flame hardend which is better,Mrmopartech