I think those are the same mufflers I looked at very closely several years ago and got all of the dimensions from the mfg.... the side outlet is an issue. You would have to modify the front hood support considerably or rework the muffler to front discharge to make it fit. I do think it could be done but, my solution was $20 and two hours of labor, all in. My gx620 is about worn out... I keep thinking about the Predator as a replacement, has anybody successfully done this? My big hang up has been the charging circuit, the gx620 in my Terramite has the 20amp coil, and the predator I am fairly sure only has 6 amps. That is a deal breaker for me, since I use mine for snow removal most often in the evenings.
Todd