i don't see any reason to play with the factory waterways.
in fact i have seen more dry-decked engines with big problems than anyone would believe. generally i say "dry-decking is the solution, all we need now is the matching problem".
i don't think sending more water to the end of the block, picking up more heat from each cylinder, and sending it back through the whole head, picking up even more heat, would be of any help. best to let the hotter water rise at the cylinder it picked up the heat and carry it away, i think.
the newer 12G940 head already have some brass restrictors fitted (don't have older ones to compare), i would say the factory was aware of flow speed and distribution.
and a small note: got an overheated head some time ago to rebuild. 2 of the unleaded valve seats came loose. guess what cylinders? right, #2 and #3.
