Some have not had good results with those aluminum radiators fwiw
I’d change the tstat and get a fan shroud fanned up ASAP. Maybe wait on the water pump until a new thermostat opens and tests your fan shroud.
it’s worth a try but boiling on shutdown has some cause for pause.
is your catalytic converter plugged? Is there cat chunks in the muffler?
have you had an A/F sniffer test to see if you’re rich or lean?