'35, need electric fan help

[AnthonyG]

Hi Brian, I wish I could fit the 15.5 in fan, 4" more on the dia. is 40% more fan. Pretty sure it's over heating, as you indicate I do hear it boiling in the radiator while expelling the coolant from the overflow tube. Block was checked for clear water path, cracks etc., prior to build as part of the cert. to make sure it was a good block. On flat ground the car did fine while moving. The last hill prior to my driveway is a long steep grade ( 2 miles ) got up the hill and into the driveway when I saw the steam, shut it down and went to the front to listen to the radiator which is when I heard it boiling. Not much traffic on the drive so I didn't idle much. I let it cool down completely and then fired it up and let it idle to see if it would over heat in that scenario and it did after about 20 minutes. Lazer thermometer sounds expensive, where would one get it from? How much $ approx also?
Thx for taking the time to think about it.