ORIGINAL: nonstoprc
6 1/1" for standoffs probably is too long. Can a plywood ring be constructed to extend the firewall a little bit so that shorter standoffs can be used? I am worried about the amount of twist force generated by the engine.
I think he's referencing a total "firewall to backplate" dimension. Most all of the GP 27 - 33% ARFs planes are somewhere in the 6.5 - 7.25" total.