You are correct RESA, that the aircraft ran on its wheels right along the extended overrun area until it reached the localiser antenna, at which point its undercarriage was whipped out from under (as per design intent, without rupturing the fuel tanks) causing it to belly flop, dig in and break up. Your description of building up the ground to install the localiser helps explains how this might happen due to softer ground. As to loss of directional control, the aircraft left the runway veering slightly to the right, but it wasn't that far off. That suggests the loss of engine power (if any) would have been to the numbers 3 & 4. The tyre tracks up to the aircraft going onto the grass suggest the tyres were all intact up to that point and the 'dotted' skid marks are typical of anti-skid system operation. It certainly appears from the wheel tracks that the wheels were all intact and working up to the time the gears collapsed.