The flathead was a low pressure system for the coolant. I have the original radiator in my 52 F6 that has been a constant problem. It has a 289 in it and when I put on a standard cap 13psi, EVERY leak showed up. The old inlet and outlet that were capped off each leaked, then the tank would bulge and leak at the seams. I soldered 2 copper rods across the inside of the top tank and that stopped the seam leaks. Measure how much room you have for a NEW radiator and start a search on Amazon.com Another consideration is the flatty fan sat a lot higher on the engine than the 289. If you put the engine in as low as mine a electric fan should solve the fan issue. If i had a time machine I'd bought a big radiator and been done with it. Good luck.