"In the early 60's, when Chicago was off 780 for maintenance on Monday morning, the 50 watt AFRTS station at Ramey AFB, Puerto Rico often visited Cleveland, Ohio. They had an 80 foot wire antenna hung from a communications tower on the base."
Sorry, but for the details provided that possibility is not supported by Physics even for one occurrence, let alone "often" ...
That station was well-heard by DXers in the Northeastern United States in that era. Two friends in Cleveland, Tom Arko and Ed Krejny (a senior design engineer at TRW) also heard it and had it verified by the station. Ed and I both used Hammarlund HQ-180 receivers with tuned loop antennas.
I have written verification of that one, along with 1 kw WUNO-1320, 500 watt WITA 1140 and 250 watt WHOA from San Juan / Río Piedras as well as 500 watt WABA 850 from Aguadilla, 1 kw WIVV-1370 from Vieques, 1 kw WISA-1390 from Isabella and several other low power stations from Puerto Rico all from around 1961 to 1962.
In Cleveland we also had 250 watt KIKI 830 from Honolulu quite often. But we did not have the opportunity, due to congested channels, to hear 100 watt stations from New Zealand and Australia and Oceania such as Eastern DXers in the 30's and 40's and even early 50's had a chance to hear.
In the reverse direction, I put my own HCRM1, licensed to 570, on 565 for a series of Monday morning DX tests and heard from over 30 US DXers everywhere from New England to Ohio to Illinois to Colorado to California as well as New Zealand. Because of being off-channel, we only ran 500 watts for that set of tests.
When I bought HCSP1 in San Pedro de Amaguaña, Ecuador in 1967 and moved it to Quito, I found a bunch of reception reports from the USA and Europe. It had been running about 100 to 200 watts into a 100 foot longwire (inverted L) only about 60 feet above ground on 595 kcs, a total clear channel everywhere.
As a DXer from Quito in the 1964-1969 period I had a number of openings that allowed US Class IV stations with 250 watts to be heard from Minnesota, the Dakotas and Montana as well as many more that were not as far away. Some were nearly 4,000 miles away and many were 100% intelligible.