That thar is a shift yoke cover you're in need of. (See red arrow my on pic.)
I used to have a link saved from a parts dealer for my type pictured, and wouldn't ya know I can't find it. But from the looks of your pic it looks like your missing some grooves for allen screws and a lil different set up on the reverse gearbox. Maybe this one
here. Any way once you get the sleeve, cover, spacer whatever in place, it will take up the slack you're needing for reverse.