This can be accomplished with the rough sponge sanding block
Soften smooth side edges of slots
This requires the first roughing with the pink bullet dremel bit followed by the brown mushroom head buffing bit.
Round corners to match clamp block radius
First mount a clamp block to the top strap and then, using the sponge sanding block, round the top strap corners to match the radius of the clamp block.
Process panel Top Straps: