Hans- The Kadet MkII was my very first airplane, and it flies great, and was an easy, straightforward build. A .56 Saito is more than the plane needs, but there would be nothing wrong with using it; as said above, just throttle back. I had a Tower .46 2-stroke in mine and it was a lot of engine for the plane. You could probably get by with a .40 Saito and have it fly the basics, like a trainer ought to, but I would do this:

Take about 2/3 of the dihedral out of the wing when you build it. This plane is an old design, and can be built and flown without ailerons especially with the amount of dihedral it has. I built mine with half the dihedral designed in the kit, and wish I had taken more out of it. This plane has a fairly short tail moment, and will turn very quickly, and also has a sensitive elevator, but it is very stable and will fly fairly slowly if you want, but with power and a hgih pitched prop, will haul butt, too. Put the .56 in it, and have a ball.

Just don't try to fly through any 1/4 scale planes as I did with mine, you'll lose. One of my friends was flying his 1/4 scale Cub, I was also in the air, but thought I was above and behind him as we approached. We met at about a 30 degree angle, prop to prop, and my Kadet became balsa confetti; he was able to make it to the runway with a broken wing root and cracked fuselage, but all that was left of mine was the tail feathers. I got the engine back that day, but the radio and servos landed in a cedar tree and I didn't find them for a year, the receiver still works!

Good luck on your build. Ken