The landing gear wires should have a short opposite bend at the end of them, which pokes up into the fuselage. Then, when you fit the wires into the slots, and screw down the plastic clips, the gear cannot rotate. If the part of your wires that screw under the fuselage do not have the bend that goes up into the belly, you may want to call Horizon and ask for a correct set. I don't think you want to bend that stuff yourself.

I don't have a diagram for the fuel tank, and mine was a RTF, so I didn't assemble it myself. You should have two brass tubes coming through the stopper. The top tube is the vent, and goes to the muffler. Inside the tank, that tube should have a bend up towards the top of the tank. The lower tube goes to the needle valve, and on the inside of the tank, to the clunk. If it is not pre-assembled, then you have to make sure the tubing is cut to length to allow the clunk to reach just short of the back of the tank.

Good luck