I have a '58 235 that was overheating with in 15min of idling. I tried everything I could think of. I replaced the thermostat 3 times and replaced the radiator with an aluminum one. I pulled the water pump out for the 3rd time to inspect it again, and this time I bought a new one. I noticed a hole on the new pump I had not noticed on the old one before, then I looked at the block and the hole was barely noticeable, so I picked out the hole and found it was full of crud that came out and made a passage up into the head. Make sure yours is clean.
Cleaned it out and problem solved.
