My sketch on p9 uses the same vertical engine CL that Eric recommended on p1; 2-19/32 from the bottom. Side offset is closer to 3/16 (5.375*sin2).

Hot Rod Todd - I forget the standard option on the OS120 is long extension or no extension. The latter I think will put your muffler exhaust outlet in the tank/battery compartment, and the muffler may actually interfere with the T-mount supplied with the kit. But I don't think you need to be that close; my Muffler sticks out about 1-1/2 inches. If you cut the long extension (2") down to about 1/2" I think the muffler will fit with a relatively small cut in the firewall. Let me know how it works out. I have a second Quest still in the box.