Pretty simple, really. Just don't build in the mounts for the retracts.

When I got the fixed gear, I held it next to the plans with the wheel mount part of the gear in the right place and marked on the fuse where to mount it. Then I built the mount into the fuse. I used a 1/8" plywood plate glued to the fuse sides and reinforced with triangle stock. The sides were also reinforced above the gear mount with lite-ply.

I chose not to split the gear. I assume splitting the gear is done so the legs will clear the sides and pipe tunnel. I built the tunnel around the gear instead. I left about a 3/16" gap between the top of the gear and the fuse sides to allow for flex in the gear. I plan to seal this with silicone sealant after covering. I believe the one piece gear will be much stronger and less prone to breaking through the pipe tunnel on hard landing. (I'm bound to make one someday!)

It still needs a little cleaning up, but here is photo of it. Sorry, I didn't take photo's of the internal installation.

Also, in case anyone is following the progress on this plane, I have made some lately due to some recent bad weather that's kept me from flying. One wing is now fully sheeted and the cowl mounting is about half done. I'll post photos another time. Construction is nearly done!