Dave, the bolts go through the top and bottom plates and through the gear itself, all of which is drilled and tapped for a 6/32 screw. I install them from the top down, and only use blind nuts inside the pipe tunnel where it's exposed. The outer bolts are just tapped straight through everything and tightened up. So far about 1500 flights and no failures of any kind, it's almost overkill. But you won't rip a gear out without taking half the fuse with it. The spacer plates are a/c ply, sanded to slip fit the gear. It should be snug and shouldn't wiggle much without bolts. Don't use anything less, it'll split. I know this for a fact.

Atilla, The thrust angles sound ok, mine is set up with 3 1/2 deg right and almost 2 degrees down. I would also ask what size prop you are using, as this also has a great effect on the slipstream. The only time I have ever seen the symptoms you describe was on a plane that had the vertical stab and rudder tilted to one side. I'm not suggesting yours is this way, but it's just one more thing to check. One thing about right thrust, if you set it to where vertical pulls are perfect, negative pushes will require a lot of rudder. It's all a balancing act.

-Mike