Wrangler1
I have buildt two of these planes and never had to do the mods you are doing. Sounds to me like you are compensating for a different problem.
I know of a few flaws with this plane. One known issue is that the plane CG's at 120mm but flys nose heavy and glide poorly. This is usually caused by the fuel tank being too far forward.
The two planes that I have buildt have had a mechanical stop infront of the fuel tank compartment. except that on my first extra it was not in place causing me to mount the fuel tank too far forward and causing a nose heavy flying condition with poor glide performance.
I later figured out that the fuel was to heavy as the planes CG was correct. So, I slid the tank back a few inches therefore correcting this problem. The factory should have this wooden peice in place to prevent the tank from going to the firewall, it should be @2 inches back.

You though, are having tail heavy issues. If the CG is at 120mm and balanced upside down and level, then the problem is most likely with the Ailerons being slightly in the up position next to the fuselodge. check for warpage. if so then have someone help you get it out. A simple test to see if this is the cause is to turn the clevisis in one complete turn. this should pull the ailerons down a tad. test fy the plane and see it the tail stops dropping when the engine is throttled back. do this as many times as needed. one turn at a time between flights.
of course ,first, undo all of of your mods such as down thrust. don't do any hot dogging until you are satisfied the plane flys right. Down Ailerons next to the fuselodge will act like down elevator. If the plane flys better after readjusting the ailerons, then, again check for warpage and correct centering. I accidently had this problem and found that one turn down on the aielron clevis corrected the tail dropping issue when the power was reduced.

A word of caution!!! do not adjust the ailerons too far down. Just enough to where you can tell that they are drooping a bit.

I hope this helps you out.

P.S. I am using a 2cycle engine which probably weighs conciderably less than your 4 stroke. therfore, nose weight should not be needed. Always move things around instead of adding weight. With a 2 stroke engine upto a Supertigre .90 the battery will mount on the battery tray with the cowling on. The battery will be mounted at the servo tray with the cowling off. This again tells me that you are not tail heavy with a 4 stroke engine. If anything, you are nose heavy already. That is why I am certain that improper aileron adjustment or elevator adjustment is your problem.