Thanks for the tip Calflyer! I went home at lunch and test fit the Saito 120 in the supplied 90 mount and it fits snug as a bug in a rug. Now if I can just figure out the bag of supplied screws and such. I am hesitant to moutn the engine until I get a few more runs on the bench with it, just to get the break in and tuning set. I have only put a tank and a half thru it so far (10oz). The first tank was entirely below 4000rpm per manual instructions. The second was a little higher with short bursts to full throttle just to hear it roar.

In the midst of writing this post, I recieved a reply from Vectorflight Support on the motor moutn question. Super fast! Their answer included several pictures of customer installations of 4 stroke engines, and one of a 91FX, "just in case". the next paragraph is a snippet from the reply...

"People have mounted 4 stroke engines both sideways and inverted. Inverted mounting looks very nice, but it requires rotating the engine mount, and obviously this will mean drilling new holes, and plugging the old ones. Sideways mounting is straightforward, if you don't mind the engine protruding out of the cowl a bit. We are not sure if you will be able to fit the Saito 120 in the provided mount, but the beams on these carbon mounts can be trimmed very carefully using a sharp knife, as long as you do not remove too much material and weaken them. Also, the mount is somewhat flexible and can be pried open just a little bit. The combination of these two things might allow you to use the Saito 120, but if not, we would recommend going to a bigger mount. Dave Brown does make a 120 size mount.

Please use struts on the tail plane for added security. Also please do not solely rely on the fin lower extension to assume the fin is vertical. You may have to trim the extension from either side to make it accurately vertical."