[rotorwrench]

Cylinder heads are also somewhat of a limiting factor on bore size and some on overall width too if you still want things to look symmetrical utilizing OEM or aftermarket heads. Basically it just has to look good and somewhat original with them on there. If the heads are changed to fit better, the design may lose some of its popularity. That would put it back into a proprietary situation.

Valve bowls & port design have some limitations with the water jacket dimensions but a different way of machining for guides could be a big help in that respect. Some folks may prefer the OEM modular valve arrangement and some may not.

The Big Cad V8 is like a 337 in size. Having the exhaust come out the top simplified the block design but complicated a lot of other things too.