Request Modified Cannon Tower

This should be quite easy for those who do geomerge and stuff, but it is downright impossible for me. Basically, what I want, is the Cannon Tower modified, so it is basically just the cannon section so it looks more or less like the following:



If possible, keep the turret bone so it can rotate if desired and the actual cannon could be like the head or something, so the cannon could point upwards, :). Thanks a lot in advance.