Get yourself some 1/4 scale turnbuckles....they replicate screw type binders very well plus they are strong enough that you can snug down the Tamiya chain rather tight to hold your tractors. All u have to make are some S-hooks for the ends and you're all set!
Just Google '1/4 scale turnbuckles' to get your search started....Dubro is a very good brand that I've stuck with when making mine.
-Alex