Good on you for asking, as it is a complicated issue, but you'd never think so untill you look into it.
Cross flow heads have evenly spaced inlet ports
The detachable heads for the Argie and Aussie 2v engines, and the log heads, have a non equal phasing.
The intake on the four cylinder HSC is equally phased, but on the six, it is non equally phased
If you were to use HSC heads, you have to run the US style log camshaft, and theintake ports to cylinderss 3 and 4 must allow the exhast ports from 3 and 4 to be grouped.
If you do it any other way, the ports will be out of phase.
I've got to get my website up and running. It's hard to explain unless I post DGR8TIM's pictures of the HSC head.
If it was as cut and dried as cutting up two HSC heads, I'd have done it already. The clincher is what happens at cylinders 3 and 4 with the exhast ports