Beltfed,
If you post your question on the VCCA forum you'll likely get the answer from Gene Schneider. I think he had an entire career as a Chevy parts counterman and this is right up his alley. Chevy heads had a variety of raised shapes cast into the bottoms of the vertical ends. For example the "Fuelie" heads had the rectangle with double humps cast in. The "Power Pack" heads had a rectangle with an upward pointing triangle above the top of the rectangle. More specifics about heads are unlocked using the casting numbers.
This site
https://www.mortec.com/castnum.htm shows casting numbers and other data for many Chevy heads.
This site -https://www.enginelabs.com/news/quick-ref-small-block-chevy-cylinder-head-casting-numbers/ says "Casting number 3795896. Manufactured from 1963-1965 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72Ë intake valves and 1.50Ë exhaust valves. 60cc Combustion Chambers." but the year is wrong for your '57.
Here Chevytalk addresses your exact issue
https://www.chevytalk.org/fusionbb/showtopic.php?tid/276171/There is a ton of information out there.
Good luck!
