PeteJoMan, I figure you have the plane already. I used a Dremel and removed the ply floor that is in the retract bay. Then took the hardwood that came with the kit and sanded it a little thinner so that the retract would fit between them. I set in the wood (Dry) to check fit and angles. It took a while but I was trying to not have to touch the spar. They will fit pretty nice just run the rear air line through the hole that is in the spar but I didn't have to touch the spar. I felt that it would weaken the wing if I did. Then I epoxied the hardwood to each side rib and the sheeting. You will notice that the ribs are ply in the retract bay and very strong. To keep the max wood available on the mounting blocks I cut grooves in them where the screws are on the side of the 615's. They do fit good when all done but did take a while to get the angles right. Then I put 7/16" Robart legs and 4" Robart scale wheels on them.