It might fly OK on that, on those length lines.

The photo of that engine shows that it is definitely the OS 25 Max.  It is a non-schneurle engine like a little brother to the OS 35S  from that same era.  It does not have the power of the OS 25 FP, but it is an ounce lighter.  I used one on the two Pagan's I built several years ago for OTS.  Those models had a 46" span, 364 sq in of area, and weighed about 24 oz.  For OTS, it was like driving a little sports car.  In the air, it acted like all it wanted to do was what I wanted it to do.  Flew on about 0.012 solid 58' lines, eye to eye.  Placed at a number of contests, including the Nats and VSC.  I ran it without a muffler, though OS had a muffler for this engine.  I did get a few complaints about noise.

The best prop I had on it was a narrow blade APC 9.5 x 4.5.  Unfortunately, that prop is no longer available and the current APC  9.5 x 4.5 is really thick and heavy and does not work nearly as well.  The next best thing may be a Rev-Up 9 x 5 or  9 x 6.  Maybe a Zinger in one of those sizes would work but thin the blades a bit.  I had a carbon 9.5 x 4.5 Bolly from Randy Smith that worked and probably would be better than the Rev Ups of Zingers.

Keith