Shiny new one
So it came to fit the new one, simply a reversal of the removal - yeh right. I got it in OK but the outlet flanges were about half an inch away (too long) from meeting up with the heater valve, there was no way it was going to fit. Wrong matrix?
Looks OK to me
So I tried to put the old one back in and it's the same 1/2" out. I'm stumped as there doesn't seem to be anyway anything could have moved, it's all solidly mounted.
Had enough today so I'll think on it and try again tomorrow. Any and all suggestions would be welcome.