THe toyo 3k (esp early ones) are a strong motor. The blocks will take more boost than ought be possible (at least the ones I've played with - mid 20s boost and no intercooler, wandered into enough detonation to pop a head gasket and take a chunk of the head with it, but the block didn't incur any damage whatsoever). The 4ks generally have thinner bores and are less happy at higher rpm and or boost levels.

You would think (I know I certainly did which is why I played with toyotas at all some years ago) that being a 'slant' motor that the k series heads would flow more, since they are essentially a semi down draught head (if you look at port angle vs bore angle) - but in practice afaik the well ported big port (I suppose gx and then oval port a14/15 heads) datsun heads will outflow the bigport 3k heads (of the factory toyo heads, the best is the early 3k head, bigger ports and valves, and room for poirting - easily identifiable by a welsh plug on the back of the head instead of a bolt on plate and heater take off hose).

Another comparison that (imho) shows the datsun heads are better, is that I know of sc14 supercharged 5k (toyo 1.5) engines, that ran a 1:1 drive ratio and got over 15psi (close to 20 at >7000rpm) boost. The blokes here that have a14/15s that I can recall mentioned something more like 8-10psi from the same drive ratio - less boost means the head is flowing more, letting more into the cylinder, so less backs up and the inlet manifold pressure is lower.

the 4k toyos in the 'square' early 80s corollas (with 'hi-cam' badge on the boot) had dished pistons and a shallow chamber head, so using the early 3k head (flat pistons, bigger chamber) you end up with around 8:1 compression - hey presto cheap turbo friendly combo.

So ultimately the datto (imho) has more potential for power NA, which is a true test of power potential in the strictest sense). Having said that, the bloke has obviously put some serious time into the build, and deserves a lot of credit for that to say the least :) Still and all, it seems like a lot of trouble when the same result could be had from an engine that essentially is the same family as the original.