RE: retracts on a rapier delta?
Your nosewheel is too far rearward. Refer to the c of g shown. The nosewheel needs to be in front of the c of g. approx at the front of the fuel tank. You could block off the bottom fuel tank access hatch with beech ply and make a new access at the top of the fuz. and make the cockpit removeable to accomodate this.
The rear wheels should be far enough back to allow the model to rotate at takeoff and a healthy 'nose up' attitude when landing. This model at slow speed needs a predominant nose up attitude due to its delta wing configuration. If you make the rear wheels too far back it will impede this action!