For the grill cloth, I use an aluminum siding tool that has a long wide mouth that grips about 4 or 5 inches of cloth. I then pivot the tool on the edge to get it tight.
That is exactly what I ended up doing, but with a quick clamp. The siding tool would have been much easier because it is so wide. I will have to pick up one of those for the future.
Is that brace just glued in, or are there screws going into it from the front of the baffle ?