Here are the reasons for my questions;
I'd check your timing again. excessive retard will make the engine run extremely hot. rev the engine and make sure it advances.
check your plugs. if they are loose, it'll make your exhaust super hot, to where your exh. manifold will glow.
if you ever used prestone flush, any remnants will make the coolant foam up and overflow.
How do you know your rad cap is good? a loose spring will cause overflow and air bubbles in your system, causing temp spikes.
With all the tips everyone have given, you should be able to figure it out yourself now. Good luck.