Loud pop and sputter on WOT? 68 318 Barracuda

The idle fuel mixture screws will shut the engine off if closed (screwed all the way in). When adjusting idle fuel mixture I'll set them at two and a half turns out and then close them until vacuum drops, then back them out a quarter turn. I do this after setting initial timing and having the hot idle speed adjustment screw all the way out so the throttle blades are closed and it's fully using the transfer for idle. I'm reading now this is what's incorrect. Factory spec initial timing is 10 deg btdc but I've read with modern fuels in an engine with some wear it's better to just set initial where it's happy.