This may be a bit old, but I didn't have a YS 63 lying around so I stole an OS 61 from a twin and tried to see if it would fit in the cowl.

I also kept the engine as far back as sensible to help with the CG later on. Although the airplane is billed as a 52-70 4-c ship the cowl and firewall do allow a 2-c to be grafted onto the front.

I rotated the engine until the std mffler was centered below the fuselage. I considered the inverted option but it put the carb too low for the available tank position. With the muffler at the bottom the cowl could be opened up to both clear the muffler and allow a ton of air to exit the cowl.

The canted engine took out less cowl material and the head tucked in reasonably well.

To do all of the positioning I bolted the engine onto the supplied mounts first. Then the whole assembly could be moved around until the desired bolt pattern could be established for the rear of the mount. The clear plastic cowl "tool" made it very easy to find and cut the openings.

I put a temporary balsa plug in the tank-hole in the fire wall to draw reference lines for the center of the engine. Then I drew new "center" lines to match the angle selected for the cant of the engine. The supplied engine mount just made it inside the cowl. The metric blind nuts were removed and replaced with new 6-32 nuts and bolts.

Regards,

Eric.