Hi Simon,
Sorry I have no measurement written down, only a couple of drawings. However all is not lost, which given measurements I have already taken of the U 534 I am less inclined to trust, I feel the need to make one more visit to the U 534, given her state of disrepair on my last visit it will not be a happy trip but I need to take a few more measurements and I have a better way of photographing the 3.7cm than previous.
They is a C38 in the indoor museum area which I can measure the base, it is a single mount but I am pretty sure that the bases were the same dimensions. Not sure when that will be, maybe Easter. If there is anything else that I maybe able to measure/photograph feel free to ask.
Regards
Jon