That seems like too much weight to me too. I had one with an OS52 four stroke that I was able to balance without anding any weight The 52 is only about two ounces heavier than the LA. After reading your post, I found a back issue of RCM with a Venus report in it where they used a 46LA. They said in the article that they didn't add any weight.

The manual suggests starting at 4-5/8" back from the leading edge next to the fuselage for a starting point. I think mine ended up at about 4-3/4" back. I used the supplied pushrods, but changed the tailwheel for a Sullivan. I don't know for certain, but I think the Sullivan probably weighs about the same as the supplied unit.

Are you sure you are measuring in the correct place, just next to the fuselage?

By the way, don't let the CG get too much farther back than the manual suggests, it goes from a smooth flyer to a flying squirrel pretty quickly!

Larry