Just had my 289 C -code rebuilt to stock specs.with mild cam.When I drove car home 4 miles from shop, air/gas bubbles were coming out of overflow tank upon getting there.The Radiator upper reservoir was empty and over flow tank was full.Also mechanical temp gauge fluctuating. What really bothers me is the coolant smells like gas/combustion.Rented block test kit for coolant gasses and test came out OK. I would think head gadget breach but my test does not confirm. The builder will make good but it pissed me off.New radiator,water pump,thermostat 180 ,new hoses but builder LEFT OUT lower spring from old lower hose. Any ideas? Are engine block test kits for coolant gasses accurate.Hell when over flow tank sound like a tea kettle it sucks.No problems in coolant dept. before rebuild.Thanks in advance.