I would think the two tongue slots on the I and J would be perfect for two tongues. Those slots are made for a three abreast with single pole usually. I think mine is just over 36″ apart. You would just have to make sure the three horse evener fit the spaces available.
I run an unusual neck yoke attachment. I use a slip hook with a safety clasp on the neck yoke and an eye bolt on the tongue. I use these for regular neck yokes as well. When I am baling with four I have one snap on neck yoke for one team and another for the other two. Both are hooked into an evener like bar, mounted on the tongue in front of them. That way all four are pulling back, or holding the load.
If you look at my web album you can see some better pictures of neck yokes with snap hooks. picasaweb.google.com
Try the album marked “making hay”, it is down a ways, about seven rows down.
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