How Necessary is a Power Steering Cooler and WHERE to Find one for 5/8 inch hose?

As a followup to an earlier question about 1959-66 TRW pumps and systems with them, I now ask the Learned Elders,

1.) How vital is a cooler for the power steering system?

and

2.) if the answer to 1.) above is "significantly" or more, then WHERE should I look for a cooler meant for 5/8 inch hose?

This latter issue bugs me! I stupidly ordered a cheap shop branded cooler from Retard Auto Parts, got a cheap little Hayden meant for '67 and more recent stuff with 11/32 inch hose to go with...

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