Running without a thermostat ok?

Your engine isn't overheating until it boils over. 220° isn't overheating just because water boils at 212° in a pan on the stove. Every pound of pressure from your 15# cap adds 3° so instead of your coolant boiling at 212° it doesn't boil until around 257°. Using a 50/50 mix of coolant adds a few degrees to the mix also. Hot ambient temps, extended idling, and working an engine can cause the temp gauge to rise but until it boils inside the engine and boils over it's not overheating.