RE: .28 in a funfactor? oh dear....
Make the wheelie bars long enough so that they will stop the truck from flipping over. But the added weight to the back of the truck could possibly cause it to wheelie even more.
You said that you were having trouble with your half shafts. Have you thought about running buggy wheels? You can use the Romulin adapters on the T-Maxx hexes and they weigh 130+grams less than the stock MT2 wheels and tires. I am using Racers Edge white spoke buggy wheels and Proline Nuckle 2.0 tires and they weigh 133 grams less than the stock MT2 wheels/tires. The weight savings alone would take alot of stress off of the half shafts.
rolland