Fascinating !
Couple of questions/points. It looks like you are running the engine with the cut-away rocker cover fitted, how much oil gets thrown around ?
Re carb, I am not sure I would try bending mazak, it is such an unfriendly material. I have found that plastic metal sticks very well to it , maybe you could build it up and machine the plastic metal ?
Re water leak, have you got a crack in the head around one of the internal exhaust castings ?
When refitting your headgaskets, do you soak them before re-using? I know there are mixed views about this, but I have often re-used the copper/asbestos gaskets without problems, but have always left them in a bowl of water for a day beforehand. What is the state of the central stud post ? They can be very messy !
Good luck with the carb and if you want a new headgasket I can help out ...