You can run 8 with the 2.5 but tight. I have ran them for two years with no problems on a 2.5. 20/49 OR 20/51 gearing and would go with the 20/51 (2.55) as this seems to work good. I went to belt drive with (2.52) as i kept breaking chains when i went to the 174.
After you extend tunnel keep snow flap as long as possible for cooling as i cut mine first and had to put the longer flap back on .
x2 on the syncrodrive I am also planning to do the 174 but with a 3`` track and the drop and roll, the syncrodive is easy to work with the drop and roll just a longer belt and a new cover.