The oldie - moldy trick - is to see if you can find the cylinder that is "missing". Usually by pulling the plug wires one at a time. When you find the one that doesn't cause a double miss - you have it identified.
Change the plug wire on that one with a "spare" if you can - see if it has a high voltage leak. Sometimes can find a bad wire by watching it run in the dark (with your hands in your pockets).
A bent pushrod (due to a sticking valve) can fall out and cause a miss in one cylinder. Happens fairly often on engines that sit a long interval between use - and has had junk modern gas in the tank.
Which carb is on there -the '57 Ford Holley or a later 4160? A 600 cfm 1850 is often sustituted and fitted with a pretty siff secondary spring.
I think I'd try setting the timing up to 10° initial - these engines are hurting for lack of low rpm advance.
Steve Metzger Tucson, Arizona