The cowl on the Spit is very narrow, and the 90SP is a tight fit. The 120 may not fit. Be sure to make careful measurements first. Also note that the drawings with dimensions that RCV has, does not include the carburetor. The mounting plate of the 90SP barely fits on the firewall at it's original height and width. You do have to extend the firewall box forward to accommodate the 90SP. If you do use it, I suggest getting the engine before building the fuselage, and carefully measure it's mounting position, then cut out new parts that make up the sides, top and bottom of the mount box. The mount box sides and wing saddles are a continuous piece and it would be best to cut new pieces from the appropriate ply for best structural strength. I build my fuse before figuring the mounting of the engine and had to add pieces to the front of the box. I ended up using some carbon I had, to wrap the box for strength.

Scott