I didn't have to do any modifications with the OS 160 FX. I did have to cut the cowling for the Pitts muffler pipes but not too hard if you have a Dremel tool. CG was perfect, as the directions for this engine. No weight needed on mine, but you should check to be sure.

I am using a APC 16X10 composite prop. Son using the same and we really like how it flies. I practiced taxiing up and down the runway before I did my first flight. Be careful if you do this with any wind because she will want to get airborne on you if you aren't watching it. The Giles wants to fly.

I had my instructor do the maiden flight to trim it out for me. He has 30+ years experience, mostly with larger airplanes. I had flown a trainer and an ultra stick in sequence before the Giles. I also had access to G2 flight simulator and the add that has the Giles. It flies much like the simulator. Would recommend you do same if you have access.

As for flight tendencies, the Giles is gentle and user friendly, but much different than a 40 size airplane. You have to fly the Giles. Meaning, use plenty of power for take off and don't try to force it off the ground. Once in the air you can back down to 3/4 or 1/2 throttle to get the feel for her. I did figure 8's and standard left and right turns just taking my time. Get the feel for her.

On landing fly several approaches to get the feel for the speed. Be careful to not approach too slow because she will tip stall or snap if you come in too slow. On my down wind leg I slow to about 3 maybe 4 clicks on my Futaba Super 8 transmitter. On my base turn I let the nose drop and bring the throttle down to 2 maybe 3 clicks to set up for final with the nose in a down attitude. On final let the speed bleed off being careful to not get it too slow. This was difficult for me and I had several missed approaches before I got it right. She will want to soar on you if you come in too fast.
Once you get the speed right she will flare nicely and settle right in for a nice three point landing. I ran off the runway several times before I got it right. A little tail waggle helps to slow it down which you will mostly likely need. You can practice this too when you practice taxiing up and down the runway.

People in our club say it's not as likely to snap or tip stall on you as the CAP. I have never flown a Cap so can't say. Just watch your speed on your landing approach.

Hope this helps. Good luck and have fun.