well, according to my research, the stock Stratus canopy cutout that comes with the kits (Version 1.4 of the Stratus Manual) has quite a large cutout.
you can see the cutouts in the picture below. I overlayed the stock Stratus canopy cutout with a cutout that I traced on paper from a friend's Stratus canopy running OS91/SB-18FH (thanks Artie !), and the stock cutout looks larger. So I think from this picture I would deduce that the stock cutout should fit any muffler (OS91/SB-18's, or the YS91SR/SB-19's. I don't know about the Muscle Pipe's though ?? ... )
I have not received my Arizona Heli canopy yet, so I can not declare with 100% certainty that the stock canopy cutout would fit my YS91SR/SB-19FH muffler, but I'm confident.