When I built the Miss America for the RCU Magazine review, I was originally going to use an OS 91. It was installed, and the cowl was cut to fit it.

Then I got a scale exhaust stack from KeLeo Creations that only fit a Saito 100 (Which is the same size as a Saito 91)

I had to make the hole in the bottom of the cowl considerably larger to accomodate the Saito, and the Saito does show through the bottom of the cowl a bit more than the OS did.

Given a choice between a Saito 91 or an OS 60LA, I would definitly go with the Saito. It doesn't stick out a whole lot, (As you can see in the photos) and the Miss A just crys out for a 4-stroke