Can you slap a 120 in a 60/90 size aerobat? Of course you can. I do it all the time.

The key to not ripping the plane apart is to realize how much power you have and then keep your left thumb under control. Throttle management is crucial when you've got 50% more power than recommended.

Balance is no problem. Use a Metal Hydride battery to keep the weight down. Then resist the urge to buy a big honking MH battery the same size and weight of a NICad. The whole point of a MH battery is that they are lighter and smaller than niCAD. So get a 1000mah 6V battery for it and call it good.

You can use smaller high torque servos in a plane that size. Get some mid size servos with plenty of torque. They will most likely svae you about .5--.75oz per servos. You can save a couple of ounces of weight there.

Use a smaller RX. The Hitec 555 is an excellent RX and it'll handle 5 or 6 servos with ease. It's got all the range of a full size RX, and it'll save you an ounce or two.

Scrap the stock muffler on the TT120 and get a Macs pretuned muffler for it. That'll save you a few ounces on the nose-- where the problem is anyway.

Wing loading won't be a problem. We fly planes like that EVERY DAY up here at high altitudes. It's normal and they fly fine-- even in the thin air.

Just keep your thumb under control and you won't rip it apart. Vertical performance should be quite exhilerating.