Originally Posted by Dave Wilshere

It does look long. Leg length is only part of it. The trunnion length and pivot point on the frame will vary the final axle position.
main gear is likely to be fixed length, so put the gear down, wing on. Stand it on bench and see what angle it sits with the nose leg length you have.

Flap is easy. Work out where the servo spline is on the cover hatch. Mark that through onto the top wing skin. Put a 15-16mm arm on flap servo. Set it with your radio, you want the servo arm angled back at full flap, it will swing forward to flaps clean. Put the servo arm in the landing position, mark the hole distance back from servo arm centre on the wing skin. Put a pushrod on the flap with ball link. Put flap at angle you want, lay the pushrod over the mark and mark the pushrod with a pen where the servo arm hole is. Put the flap clean and mark the skin with the pushrod travel. That is the servo travel you need to set in your radio flap travel.
Cut the pushrod and add the clevis/ball link you will use.
It’s normally easier to attach the servo end first, feed the pushrod through to the flap and add fixing screw once the cover plate is in position.
Easier to do than read!