LA360 Vapor Lock, Heat Soak, OR??

“The Holley 750 dual feed was rebuilt” There is a bunch of ways that it could change how it runs. Idle mixtures not the same setting. Idle speed not the same. Float levels not the same. I don’t think it is boiling the fuel. The four hole will increase the velocity of the air. More velocity, more fuel. The four hole will probably want different idle mixture and idle speed settings. You should use vacuum gauge and reset idle mixture. Well at high alt it will boil easier.