My 4-60s balanced on the main spar. One had an OS 91 Surpass for power, the other an OS 61 two stroke. Balance was achieved without adding additional weight.

You may want to go to a larger battery, to aid in the balance. Moving the servo tray forward will help, too.

I had this same problem on my Bingo, which is the low wing version of the 4-60. You're right. It took quite a bit of weight to get it balanced, and the model flew "heavy."

In my 20 plus years of flying, the Ace 4-40 and 4-60 were my favorite models to fly, second only to the Ace Taylor Craft. I'm building one of those, at the present time.