Help with vintage snakeskin ID please!

[Allan]

The "saddles" change shape from squarish to round/oblong.

 

[Sdaji]

Thanks all! What is it about the tail pattern that makes it obviously a boa?

Boa Boas (as opposed to Boas of other genera) have distinct tail patterns. If you google "Boa constrictor constrictor" or "Boa imperator" or just "Boa constrictor" or "Red-tailed Boa" you will see examples. If you look up other Boas such as "Rubber Boa" (an actual type of live Boa from another genus) or "Emerald Tree Boa" or "Yellow Anaconda" (which is a type of Boa but not in the genus Boa) you'll see the patterns are very different.