Inline 6 sat for years OVERHEATING

[redhoss02]

Truck sat for how knows how long before I got it. I removed valve cover dumped a gallon of oil over the valves and let it sit for a day. Removed the carb and rebuilt it and thanks to a member here got a filter and fitting to connect the fuel line. Cleaned build up in dist cap, installed new battery and she fired up. Problem is she would get hot really fast. I'm thinking since it sat for son long there is some build up in the water jackets that are not allowing the engine to cool as it should. As of now the gauges are not working till i figure out the wiring so I really don't know the temperature. Are there any tricks that can be done to help open up the water jackets? I have added a coolant flush additive to the water to try and help break everything up. Should I just keep doing that?

Replaced
water pump
thermostat
all hoses