I had to think about this one a bit. The first suggestion is to
stop changing parts and find the root cause.
You definitely need to verify the timing - setting by ear is virtually always way too advanced. A timing tab is a couple of bucks - verify TDC and set your initial timing to 8-12 degrees.
I suspect it's a fuel issue too. The quickest check I can think of is to pull the sight plugs on the primary bowl of the Holley and then start it up. A little splash out of the hole is fine...but if there's NO splash at all it's getting too little fuel, and if it's gushing out, too much. If the Holley was installed out of the box I'd figure the float level was in the ballpark - so either of these conditions reflects a problem upstream in the fuel system.
The only cause I can think of for too much fuel would be a pump putting out more than 6-7 PSI; your previous carb could have been flooding due to a bad needle and seat or incorrect float level, and now it's flooding because a too-big fuel pump is overpowering the Holley carb. The pump you installed was a STREET pump putting out 6-7 PSI? Easy check is to plumb in one of the cheap fuel pressure gauges from Schucks/Kragen. Anything more than 6-7 PSI is too much.
Too little fuel makes me think you've got crud at the bottom of the tank blocking the pickup or somewhere along the fuel line between the pump and the tank. Try blowing it out with a compressor at 10-15 PSI - be sure to remove the gas cap first
Wish I was there to help; may be time to get another pair of eyes looking at it with you.