I purchased a thin wall socket, it may even be one for spark plugs with that rubber inside, from Sears. To that I add a u-joint and maybe a 4" extension. The u-joint allows the extension to be put to the side of the frame tube as the assembly is lowered into the pit. Once in place enough room is left for the ratchet to be attached. Retrieval of the spark plug is the reverse.
This seems funny saying, but the earlier Hinckley bikes came with tool kits strapped to the base of the seat. It possible to get one on ebay as I did for the used Tiger I had. All and all putting together something on your own is no doubt better.