The best way to describe it would be a bellcrank, similar to what the '55 2nd series trucks have. Only this one is frame mounted rather than on the bellhousing. The from that crank, there's a shaft (that's what the manual calls it) that connects to the lever on the trans. As far as truck useage, you'll need to swap the levers from your existing transmission to make the linkage work, so the ones that are on it won't really matter.
Here's the manual pic. It's he one on the bottom.
BTW, the SM318 is the non-syncro 1st gear 3 speed, used from '55-'66 in most GM 3 speed applications.
