I pulled up my CAD drawings for the 260. The exact offset should be 10.22mm (.402") to the left of the centerline of the firewall. It is slightiy more than 3/8", but only .7mm, which isnt going to make any difference to the perfrmance of the model. Hard to imagine you can see that though.

How far off center is your spinner?

Also, remember this back face of the spinner should be on the centerline, so the front of the cone should point to the right side if its installed correctly.