Too Hot

At 55mph, in Alaska, at the same before/after elevation, you got plenty of ram-air, so the doggone rad should be running at or near the stat rating.
Unless one of;
1) the vacuum advance quit ...........
At 2500, your engine will like cruize timing in the window of 50/55 degrees. maybe even more. anything less than 48*, I would consider retarded cruise-timing. or
2) the rad is not passing air thru it, in the correct direction, lol, or not getting air in the first place, or
3) the water is not going round and round and round, lol. or
4) the lower rad hose is getting sucked flat, or
5) the rad is defective.
These are my guesses.
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BTW
My system runs right at 207, and makes enough power to go 93mph in the Eighth like that. and with one size smaller cam, went 32mpg point to point. and the engine now has over 100,000 miles on it since the last time I opened it up, and get this, I only recently changed the sparkplugs, not because they needed changing, but because I told a potential buyer that I would. Then the plick was a no-show. For me, 207 is magic.