George,

The OS 61 FSR used the #744 it was a bolt-to. This is the one that works with my later model HP 61 Gold Cup and Webra 61 Speed ( #1024). The OS 61 SF used the #744B muffler. It is the bolt-thru pattern on the SF. They are a different pattern some of the first OS 61 SF's had the muffler with both sets of holes so it would fit both the 61 FSR or 61 SF. I don't have any experience with the FX / AX and don't know.

I have used the BCM #161 and #162 mufflers. I like the #162 low DB the best. The extra volume seems to more than make up for the quieter sound. It is a great situation if you need to be quiet. I have been very happy with any of the BCM sport muffler applications I have tried.

turbo