At first I thought you had to modify the frame, but drilling out the claw on the broken simplex isn't a problem - its broken! Check the clearance for the thin nut that goes on the back. Once you get it mounted you may find you have to move the lever a lot further than you did with the simplex - the Suntour needs more cable to move a given distance than the Simplex did.

Oh, and sailorbenjamin, what is a Suntour Vista? Looks like a V but I've never seen that name stamped on one.