Help freeze plug

[kgrove56]

i put a used motor that has been sitting for many years in my brat swap over the original California manifold and carb fire it up ran fine but the radiator empty out as fast as I could fill it check the oil and all the way to the top with white milk left it over nite and still turned over pulled valve covers driver side freeze plug missing how hard it is to put in with out pulling motor out and should I rip the motor apart to find the missing freeze plug