Of course I mean to use a pair of templates. I have a cabinet shop not too far from here where I can get pretty large scraps of 1/8 3/16 and 1/4 lite ply (not that good for templates but for fuse formers and fuse sides for sailplanes) and also Formica! Formica makes good template material.
A sandwich of balsa blanks between 2 formica templates would be ideal.

AS for the guide bushing I need to be educated. I understand how it works but not how to mount it exactly. I have seen them mounted on some router bits but not on something tall like a RotoZip bit.
A RotoZip bit can be agressive even on Formica. I think they even make a Formica bit which I would not use except to possibly make my templates.
Obviously I have a lot of details to learn.

Robert