Blown and injected BB Chev Bent piston skirts

Hi all. We are running a 55 Chev door car ,blown and injected Chev on alcohol. We are having trouble with the pistons skirts bending and causing them it hit the heads. The car weighs 3100 lbs ,big chief 14 degree heads, 580 cu in Dart cast block 10.2" , 6.535" alloy rod. BME flat top blower pistons, 11.6 to one comp ratio, Indy manifold, 52% overdrive, 40 lbs boost, 1320 Enderly pump, Bird catcher, Littlefield 14-71 hi helix retro ,MSD 20, 3 speed lencos 2.25 1st gear ( will be 4 speed with 2.8 first gear next season ) 4.56 diff ratio, 34.5" MT 's , Crower triple alloy spring clutch, 1.12 - 1.18 sec 60 fts. Best et 6.88 @ 203 mph. Leave at 4500 to 5000 rpm ,change at 7700 rpm. Fuel pressure read after the run ( highest reading ). 150 lbs , Idle 8 lbs, @ 2000 rpm. Port lines come in at the hit of the throttle. Plugs NGK 5671A-10. usually coloured down 1.5 threads and just coloured on the ring face. Electrode coloured just past the turn. We do not have a computer to monitor things. We do not have fuel enrichers and do not have the high speed connected. No ignition advancers or retarders. We are not sure which bit is wrong? We are sure it is detonating at some point in the run but can't seem to stop it. The colours in the bores above the top ring are straw coloured in places. Any suggestions? Need any more info?
Cheers. Murray

 

Too much timing? when you say just past the bend on the electrode is it colored past the bend plug base side ?