If you measure the lens and the buttons. it is 84 mm which meacns that it will go into the extensionrings with some force. If you measure the lens without buttons it is 81mm. Yeah i could use it with force before to.
But this also means that the lens will be off-center, as the port is 85 mm . This as the buttons are sticking out in one direction. To be able to center the lens in the extension ring and get away the tension in the mount you need to have (84-81)*2+81 = 87mm. 
I do not think that forcing the lens and the camera is good for the camera and the lens or the housing, something will break sooner or later.
No problem to find a guy with a lathe, just call around a bit. When calling them se to it that their lathe will be able to hold somethng 115 mm in diameter from the outside. I gave the guy $35 to fix 5 extension rings.
