I think I remember this one - a Saphir II. If it's the Saphir II, it's designed for the early 1.20 4 stroke engines and has a larger wing than the Saphir (60). I built a Saphir (60) ARC recently and put a YS .60 LSRE on it. A 2 stroke engine (esp. a 1.20) may cause some pipe fit problems, as it goes under the wing and you have to cut out some of the wing skin, foam, and even part of the spars to keep it from sticking out too far. My plans had pics of a very small 4 stroke pipe, with just a little of the underside cut out. I cut a lot out and still had a plenty of pipe sticking out of the bellypan.

Another thing worth considering is the weight of the engine. If you add more up front than the plane was designed for, you may have to add weight to the tail to balance things, and the wing loading may go up. I was able to get the fuel tank near the CG by cutting into the canopy, making a cradle for it inside, and then painting the canopy to hide it. I sold the plane before I flew it. If I can find an pic of it, I'll send you one.

Good luck