1987 Monte Carlo Ss

I'm helping my friend with his car. He has a few problems. we removed the msd and put the stock hei back on. oh motor is 350 v8 crate motor. put a double pumper carb on holley. car pings like hell and is not at a 100% power. we have the timing backed off as far as we can go and it still pings. any ideas? oh and it stalls off the line when you floor it. if you slowly accel shes fine. comments would be great thanks

dont wanna sound like you dont know what your doing but your sure the crank mark is set? sounds to me your not at TDC with piston 1. I wouldnt light to light in a hurry or you will be replacing some rings. regardless of anything else if your perfectly timed should be no pinging if your off your crank mark by just a bit makes a huge diff. hard to tell by just what your write but thats what i make of it.