I have a 62 chevy 1/2 ton truck with a 235 six that once had the same problem. Suggested solution-go to Auto-Zone or similar store and purchase an overflow kit-shouldn't cost over $10 -and install on your truck. Also use a 7 pound pressure cap. Expect overflow after most drives but the antifreeze siphens back in your radiator instead of on the ground! This setup has worked for me for over 20 years in this Texas climate of over 100 degrees so should work for you. I am assuming that your radiator is in good shape? Hope this helps.
