I'm running an OS 120 in my Funtana 90 with no problem. The OS has a pump and carb on the back. The engine is almost touching the firewall. With this set up I have 1/8 " clearance from the spinner back plate to the cowl. I believe the spinner is a great Planes ( one I had laying around).
The original pre drilled holes with the blind nuts did not work with this configuration. I had to glue a couple 3/8 X 1/4 hard wood strips on the front of the firewall and drill for new blind nuts. This allowed me to move the cowl a little forward without the holes being to close to the edge of the cowl. I picked up about 1/4 " by doing this.
What is the length of you engine from the back to the back side of the spinner back plate? I'll measure mine and we'll compare. If your engine is old it could be big and bulky.
For example a club member has an older OS 120 and its physically a bigger engine than mine but the same cubes.

K.O.