It's great to have sliced "views" of a head casting to look at, but you also have to consider the problem of core shift and realize that head castings, at least A-series head castings, are not nearly 100% identical to the slices. Even the best head porters get surprised on a regular basis and end up breaking through the casting into a water jacket and end up scrapping a head into which they may have labored many hours.

So, look at the slices and get an idea how the heads are designed and cast, but don't ever forget that you will occasionally have to discard a head because you have broken through into a water jacket despite your best efforts to avoid doing so.

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"it's always better to be uninformed than ill-informed"

Another problem with many of these old heads now (in Oz) is corrosion. This seriously reduces wall thickness in critical areas.
Unlike in the UK where most everybody has to use antifreeze, I'd say 2/3 of Oz Minis got run on plain (and rusty) tap water for most of their life. So have a real good look inside the jackets of that head before you even start porting.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.