Classic Austin Mini steering wheel boss hub Mountney wheel

I have a customer with a MkI Midget and a mountney steering wheel. This is the arrangement with a slip-ring and the sprung contact point up the center of the column. I have his horn circuit working, but he lacks the horn button/center. He only had a non-function cover. I ordered a horn push from the UK, but the center contact in the column is quite tall and interferes with the horn push such that it can't get close enough to install. I wonder if he has the wrong hub. Can you supply me with a correct hub and horn push for this early Midget?