Hot Rods Aluminum Head circles ?

Old Offy flathead head are these circles from factory cutting or signs of work done ?

 

I dont think any of my aluminum heads look like that

 

Those look like someone machined them deeper for a large lift cam

 

Is there a way to measure that ?
Thank you

 

how high does that little triangle between the machined areas, stick up?

 

It is sloped but at its highest looks to be 1/16

 

Also, what's with the spark plug hole? It looks awful big. Is it for an 18mm plug?

Are these 24 stud heads?

 

Offenhauser V8 60 heads

 

Is there any way to stump squirrel? wont that head have lower compression?

 

It looks like marks from a non-center cutting end mill.

 

You can sure tell that the old flathead guys are gone, when no one can recognize a head that's clearanced for valve lift & size.