I thought this was incredibly interesting. I was just digging through the internet and found a guy from EU balkins region that has a "CA18DET Bible". This is a 130 page document found here.

https://www.scribd.com/document/677546023/CA18DET-Bible

In it though, he describes the head airflow with benchmarks. Really hard to read at first, but I'm sure the smart people here can. I thought you guys might find this interesting.
He also shows that some blocks have 2 holes for the oil drain from the head rather than one oval shaped hole. WHOA. Never seen one like that.
He also describes painting the inside of the valve cover with Glyptal paint. This makes the oil slide off the walls of the covers to fall back down quicker. https://www.youtube.com/watch?v=77CKFnRHA3c

I've been through that and it's good stuff. It looks like there's been some more info added since the last time I read through it though, so I think I need to look at it again!