The D-port was just a idea that came out of me reading this, http://datsun1200.com/modules/myalbum/photo.php?lid=1777 (Scrool down), where D suggests porting it that way.

I was very skeptical to weather, or not, it would break into the water jacket, and it properly will... So the idea is scrapped...
Just for fun, how bad is it to block off the water-passage above the ports?
Thinking about the good-old gigant raise tube insert, for the downdraft/high-angle intake :D (*_*')

My plan is now, (to not go bonkers)... to just enlarge the whole port by 1-2MM and raise the top by 3-5MM, depending on how thick the wall is?
My guess is that it is around 5-10MM (7MM?) when I compare the wall thickness, through the pic. by (ang94541), with the bolt, which I believe is a M10 bolt( ? )

EDIT. I talked with my farther-inlaw, here in Denmark we have a very special guy. He is a old retired man, ex-mechanic/machinist, that back in the day had his way around some motors. He was an absolute GURO! He specialised in Moris's and get this. When everyone else hit top end power, and nobody could squeeze more power out from them, he didn't want it to be it, so he designed a new head(or worked with the original, dont know all the details)... with crossflow... And made 20HP ATW more than anybody else!
I need to get in touch with this guy. If I can get him to talk, or if I got the founds, let him do wonders to my head He loved doing that sort of stuff as I understood(ad a good price), and back in the day there should have been a couple of Datsun's around up here, so he might have had his fingers in one already!