Shows what the extra capacity of a 1275 does - on the stock 998 (std head, cam etc) in my Moke, Ben's SC12 kit will make 11psi when driven HARD (makes the ol' girl bark a bit!).
As far as the water injection goes, it'll be interesting to see what Ben says. . .
However:
I cobbled together what appears to be a pretty effective system in the end, and I DIDN'T use the 'new' port on the carb-to-supercharger manifold.
I drilled a small hole into the carb (HIF6) on the
upstream side of the throttle butterfly and epoxied in a short section of 1.5mm ID metal tubing. . .I squashed the end of the tube
almost flat to create a bit of a restriction, and connected the other end to a plastic container full of water with some tubing.
The air flow will draw water out of the 'nozzle' at a rate depending on how much you squashed the end of the tube. Doing it this way, as airflow increases, water flow increases. If you put the water line on the downstream side of the throttle butterfly, the water will be drawn out by engine vacuum, so you get lots of water at idle and not much when running flat out.
Sure, you can set up a fancier system with pumps and pressure switches and the like but, apart from running the water reservoir dry, this system is almost failsafe.
On a side note, if you go this way, put the water reservoir as low as possible in the engine bay - if you put it up high, you run the risk of all the water running into the motor when it's switched off and hydraulicing the thing solid (not a good look

).
Now, let's see what Ben says. . .