F12 sickle mower working, almost

My F12 came to me with a bundle of iron that was claimed to be a sickle bar mower. These last couple of days, I mounted the thing, greased it up, made a pitman arm and fired it up. It seems to do ok, except for two things. 1) The coupling that connects from the pitman arm to the knives won't survive full throttle. It works ok at idle, but crank up the F12 and it will shake loose. The picture I took of the coupler shows what looks like a mechanism to secure it, but I have no info on what is supposed to go there, or how to secure it. 2) There is no support for the mower on the sickle arm side. Under the mower there looks to be a place to attach something that would ride against the ground (wheel?, skid?), but nothing came with it. Any advice on either? Thanks folks.

Is there supposed to be a spring onthere some place

: Is there supposed to be a spring onthere some place

Ahh, a spring between the pointy thing and the hole on the other side would keep tension on the ball. That might work! Think that was what was intended? Thanks.