You can't run these cars without a radiator cap. They have to be run under pressure or they will boil. You could still have air pockets but you also could have a blown head gasket now from the initial overheating. The only way to be sure to get all the air out of the system is to use vacuum fill equipment that pulls a vacuum on the system first to remove all the air.
It looks like we missed you on the time restraint, but look at this page it will give you an idea on how to do the job
https://www.2carpros.com/articles/replace-thermostat
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Monday, October 6th, 2014 AT 2:21 AM