1970 Z28 intake, carb, heads and air cleaner find

[ted]

I have a straight plug head 3991492 dated K30 1 with 1.94s, pressed in studs and acc. bolt holes.
Looks like Mr. Furback is from New Brunswick and I am from Quebec. Could these somewhat similar geographical locations have anything to do with this topic?? Just an idea, maybe a bad one, eh boys??
I have 3991492 and the head below 3973370 as camel humps on my parts listing.

Here is another one, 3973370 dated D23 0 straight plug 1.94s was on the same 355 engine I bought years ago.
Obviously they are not date-matched, but 3973370 is that a popular U.S. head or an oddity of some sort??
Thanks!
Ted