My avitar shows a World Models .46 Mustang with a YS 1.10 barely in front.

We race warbirds a lot here so there is plenty of experience with putting large engines in small airplanes. The WM .46 Mustang and YS 1.10 combo is popular for our Gold class because it flys well, comes with retracts installed and does not cost a lot. It also comes in many different colors and markings, Reno racer and military. With high nitro this combo can exceed 140 MPH.

The biggest problem is the weight in the nose. You can easily modify the firewall to move the engine back 1/4 inch. This does not sound like much but every bit helps and you have to beef up the firewall anyway. All radio gear is moved back as far as possible.

You should have a control horn on each elevator half and the stab should be strengthened. You can peel off the bottom stab covering to do this.

Because of the high wing loading, takeoffs and landing are much more exciting. The high weight will bend the retract struts on this plane so they should be checked every flight.

The weight of the Saito 1.25 is similar to the YS 1.10. I recommend the YS 1.10 for several reasons:

1) You can put the tank on the CG. With all the radio gear in the tail, there is plenty of room for the tank.
2) The YS 1.10 will turn more RPM than the Saito and go faster.
3) You can remove the muffler, nitro up and go really fast and loud.