273 to 340 swap

Assuming you have the oem shroud ? I think the service manual talks about either 17 1/2 or 18 inch fans for 66 as being the largest oe style fan. I havent fit mine up yet but I hope to be able to use a solid drive aftermarket 18" stainless 6 blade flex fan that I got gratis from my brother. If you arent running a shroud then put the largest fan on that will fit and not be obnoxious.