They were called a Tudor basement and they were offered by a supplier years ago that has since gone out of business. They fell out of use when the overdrives came along as they got in the way of the overdrive transmission.
We just recently installed one in my grandson's 1930 Tudor. How we did it was to measure where a Mitchell overdrive transmission housing sat on a 30 Tudor. Then we measured where it would sit if the Mitchell was configured for a Victoria as it would then be 4.5 inches further forward. With that information we constructed the basement out of carboard and made sure it fit. It was then taken to a sheet metal shop where they constructed the basement.
When we installed the Victoria configured Mitchell overdrive it fit perfectly with two inches of clearance. A trap door was fabricated into the floorboard. The basement straddles the rear torque tube section of the overdrive and provides plenty of room for tools.
Tom Endy
