Barient 28 locking winch handle?

I have a pair of Barient 28 winches on Papoose. They are the old style ( http://l-36.com/winches/winches9.htm)There is no grove for the lock of a locking winch handle to catch on so it doesn't lock . Does anyone know if the mainshaft can be modified so that a winch handle will lock? If so, has anyone done it and how did you do it? By the way, winch maintenance instructions for many models are on my site for your reference http://l-36.com/winches.php Help yourself. Allen