I have a really nice original from my '63.
I worked a while with 456Tony and then locally here in SoCal to get reproduced, but was Way too expensive.
My thought is to find a 4x4 with a "laying flat" stick like ours and adapt. I think maybe early 80's 1/2 tons had this type, I haven't pursued it in a while.
Problem with a conventional " hole in the center" boot is that the bellows keep trying to return to vertical and rubbing that low angle stick quickly tears out the center hole ...