4 Barrel on 273?

My 1966 273 has the older heads (2465315, 2532080) but not sure why (I'm kind of a newbie too), but I do know that the bolt angles are different on the intake.

I'm not sure if some 1966 273's had the had the older heads but it might be worth looking at them if your valve covers are already off.

1964-65 heads are will have the numbers 2465315, 2532080
1966 will have 2536178,2658234