Just unbolt the bad fan and replace it with a similar SPAL fan. You might get lucky and find the SPAL fits the hole spacing in your shroud. Worst case take the shroud off and re-drill the holes. SPAL has an entire online catalog with drawings for the sizes and CFM specs. Not sure what Ron Davis used for fans but there are numerous sizes that would allow you to match their setup very closely. I would not touch the radiator or disconnect any of it unless the shroud is somehow not removable otherwise. Easiest way to work in there is to remove your hood. 4 bolts and you have all the access you need.
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