Any help finding a bolster plate for it?
Depending on the job, a piece of something like 1/2-3/4" thick A36 steel will be just fine. Drill a hole in it for the job at hand. Also provides better support to what you are pushing on than the "U" shaped slot.
So along those lines you could drill a number of holes, 5/16, 7/16, 9/16, and on up which is provide clearance for 1/4, 3/8, 1/2" shafts....can drill a custom hole for whatever is being worked on right now.