Overheating headache

IMO, the pulley was NOT your problem .
A ratio of 1.3 is extremely high.
I'm glad it solved your problem, but now you may have a new one(s)
which being how to keep the belt on at rpm. So you are gonna have to keep your eyes on the gauges after/during every hi-rpm blast.
At 30% overdrive, 5500 crank rpm is now 7150 water-pump rpm. Good luck keeping the belt on.
If you have a 5-blade (or more) all-steel fan, then, my guess is that;
1) the idle-timing is retarded,
2) AND/OR the ring-gaps are too tight,
3) AND/OR the skirt clearance is too tight.

If the low-speed timing is late:
the mixture will not finish burning in the chamber, and so;
the first six inches or so, of the headers, will run very hot, sometimes even glowing red.
The exhaust ports will also run hot, transferring heat directly into the nearby water-jackets.
The exhaust valves will run hot, pushing their heat into the heads.
your exhaust system is a wildcard. Obviously, a restrictive system will back the heat up all the way to the exhaust valves. If you pressure test it, I shoot for less than 3.5psi .
Fuel consumption will be atrocious.
power and torque will be down.
Your street engine might like the following timings, just guessing;
Factory ignition timing means nothing.
you MUST have a working Vacuum Advance system.
idle-timing of about 12 degrees, with a manual trans.
PowerTiming not more than 32/36 depending on many factors
Stall timing of 20 to 28*
Cruise-timing in top gear of ~56* at 2600rpm
Cruise-timing in second gear at 30/35 mph of ~44*
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Just for reference;
The pump on my 367HO manual-trans car is underdriven , and runs an ancient rad from a 1973 Dart, plus a thermostatic clutched fan. It will idle down to 550 in gear and pulling itself along in parades at 3.5 to 4 mph....... endlessly. At idle, the pipes run about 400* +/-50.. I run Dual 3inch pipes all the way to the bumper.