Retract installation:
Credits...pics come from Kip Newby's build on the retracts and he was spot on with his tutorial on the retracts.

Before you can install the heli into the fuse, you must install the retractable gear system and servos first. Clearance between the rear of the helicopter frame and the rear retracts servo must be addressed when you do mount the heli to the fuse.

I started with the front retract for obvious reasons..it's easy to get to. A standard 9G servo will work on the front but I recommend 10g or bigger like the HS65's, prefrably a digital MG servo with good servo horns that are not brittle and could shatter.

Test fit the front retract unit into the hole. You will note a gap in the front and the retract unit will not slide completely tight against the forward part of the recess for the retract. The fit lines on the retract are 100% square, the front of the recess for the retract unit is rounded. Use a dremmel and clean the recess up so the retract unit fits squarely against the front of the recess with zero gap. The gap situation applys to all three retracts....ensure proper fit on all 3, and installation of the retract units is the same on all 3.
Now you have the gap situation taken care of, time to install them. You'll note on all three retract recesses, there's micro ply inside the fuse for the screws to grab glued to the fiberglass. That's all fine and dandy but my experience was the micro ply delaminated while drilling/installing screws. My advice is to use 5 minuet epoxy and cover those pieces of wood on all three mount places with epoxy and let it cure.
Place the retract assembly into the recess and make sure a proper fit. Mark the holes to be drilled in the bottom of the fuselage using the screw holes in the retract unit as reference and remove the retract unit. Drill the 4 holes with the proper size drill bit for the screws you will be using, then place the retract unit back in the recess to verify being correct. I used small pan head screws from the local hardware store. As you screw the unit into it's place I put a drop of thin CA on each screw, and quickly run it in....DO NOT OVER TIGHTEN. Do this procedure for all three retract units.
Installing the landig gear wire into the retract units....this is TRICKY. As noted in Kip Newby's build, screwing in the gear wire into the retract may break them. I used a #11 exacto knife, and I opened the holes where the wires thread into the retracts and I thought I had them opened enough. As I was threading the wires into the holes, the plastic at the bottom of the hole started to blush (change color). Guess what? Weak spot and it did break off right at the base rendering the one retract unit unrepairable and useless (when I landed after a test flight)....I'll get into that later. So....in my opinion (what I should have done), drill out the holes gently and carefully with a drill bit that allows the gear wire to go in very easily, but not too loose. Try NOT to have the plastic blush while drilling...it means you basically destroyed it. With it drilled out and being able to install the wire easily with no blush at the base, remove the wire, put a couple drops of 5 minuet epoxy down the hole and gibe the wire threads a light coat of epoxy. Place the wires at the proper depth in the hole and make sure the wheels are exactly straight (remove any excess epoxy with alcohol and a rag) and allow the epoxy to cure for an hour or better. This should take care of the breakage problem. After all three have cured and all is well, install the servos as required (see pics). Note: the end where the push rod connects to the retract unit from the servo is ALSO a WEAK spot...expect breakge, and make real sure there's no binding and it's as straight a push/pull movement as possible when the servo operates the retract units. Now you got the retracts in and set up making sure there's no movement of either front or rear retract servo and the well holes are opened up so the wheels do not hit while retracting and everything is nice and smooth....it's now time to fit the heli to the fuselage.