I've been having issues for the past few years with getting a 383 LT1 setup to work right in closed or open loop maf with the LS1 ECM. No matter what i do the car fouls out the back cylinders really badly. We've searched everywhere multiple times for vacuum leaks and found nothing. The o2's will just randomly go crazy and cause huge fuel swings and always foul out 7 & 8. I haven't tried open loop SD yet because it's been quite a while since I've messed with the car but I want to get the thing running right so he can run some mile events with it. It seems to idle smooth and drive fine until it fouls out the plugs in a matter of 10-20 minutes.