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Those plugs look positively nasty. I have seen MGB plugs from stock engines that had a lot more miles on them than that and they looked a lot better than that.
When you start messing with water/alcohol injection you need to be checking plugs a whole lot more frequently than 8k miles. If you get a bad distribution of the mixture you can burn a valve or cylinder in a heart beat. Just ask any of the Unlimited racers at Reno about how easy it is to blow up an engine.
Military aircraft in the piston era used a water/alcohol injection system to boost power briefly for takeoff. There was only so much you could carry without compromising gas (range) or payload (ordnance) and the engines were not built to take it for long anyway.
If you are burning exhaust valves I would suggest that you are a candidate to replace them with SS valves, perhaps even sodium filled ones, if you want to continue this experiment. (Do the valve seats while you have the head off.) Despite their racing history, MGB production engines were never meant to take a lot of abuse although they put up with more than most people would imagine.
By the time you get into an EGT, cylinder head temp and adjustable fuel mixture setup, I am afraid that you will be defeating the purpose of an MGB which is simply reliable (well, at least by British standards) transport that is fun, even at slower speeds, with a top that is easy to put up and down.
The modern day version of the MGB is the Mazda Miata, at least the first version.
Did you even install modern valve seats in the head? That is a fairly useful thing to do to prevent "valve recession".
In any event, have fun with your project.
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