Bob Hackett
I wouldn`t bolt the plate or anything else into end grain.
Make the plate 1-1/2 " wider than the slot and cut a 15/16" slot on either side to to slide the plate into and then a single lag bolt and washer into the side grain will retain the plate yet allow it to readjust itself if and when the top moves in any dimension. No end grain holding anything, a single shot lag keeping the plate from dropping out and the forces are distributed over a 3/4" wide by pretty close to the thickness of the bench top (say thickness minus 1") X 2 instead of over 4 points held by end grain threads. Much stronger and far cleaner installation as well as operation.
Now that end cap is just a support of the other end of the screw and the handwheel and is not subjected to any of the forces that originally were trying to push it free of the bench.