I am putting a 91fx on a lanier stinger 60, there is no built in right thrust, so i was thinking of putting in some washers which shim it pretty good except for the small gappage. Has anyone done this and will it be a problem?

What you're describing is pretty much standard practice. The little gap is certainly no problem. The hub will be slightly off center if the offset is not built into the firewall during construction, but the solution still works better than no offset.