Just after lift-off from RWY 29R, the acft began to pitch up. As the pitch-up progressed, the plt applied right aileron & full right rudder. The acft responded by rolling to the right with the nose falling thru. Subsequently, the plt was able to pull out before the acft hit the ground. It collided with a 6 ft wire fence which tore off the engines & caused the acft to rotate clockwise on the ground. Cargo in the acft was thrown thru the side of the fuselage. The plt exited the acft without injury. The acft immediately burst into flames & the fuselage was badly burned. An investigation revealed that 2989 lbs of freight plus a 359 lb motorcycle were being carried between bulkheads 5 & 11. The bulkhead loads were limited to 450 lbs (5-8) & 300 lbs (8-10). The max gross weight at takeoff was estimated to be 10,310 lbs. The plt reported that none of the freight was tied down.