OVERHEATING

At 3500 your Cruise timing should be at least 50>56 degrees.

I'm gonna say something that is gonna sound crazy;
Once the stat opens, my 367 runs right between 205>207* measured by IR gun, at the hottest place I can find, on or near the stat house. I have never seen her run more nor less, no matter how I drive it.
The reason for that, principally is that the huge 7-blade fan runs on an HD thermostatic clutch, which cycles between almost full slip and full drive, in accordance to what the temp is, of the air that is coming thru the rad.
The waterpump on mine is UNDER-driven in an effort to keep the belt on at 7200 rpm. And yes, she runs an 8-vane pump with an anti-cavitation plate, and all the other stuff that has been mentioned. But the rad is circa 1973, off a 318Dart.
By her trapspeed in the Eighth, she appears to be making 430hp.
But I gotta tell you the whole truth, the first year that she was on the road, I had a heckuva time keeping her cool. Even the second year. And like you, I tried everything.
Finally I took the engine down and honed the holes out another half a thou, and increased the top-ring gaps by IDK, maybe .003>.005. Badaboom, problem solved.
So, IMO, when all else fails, you gotta think about the ring-gaps. If/when you get a lotta heat in the chambers, sooner or later, that heat is gonna find it's way into the pistons and rings. When the rings swell and the ends butt, Bam! you got instant mega-friction, which makes heat.
Happy HotRodding.

BTW, if you are afraid to run a large diameter, hi-attack angle, all steel, 7-blade, clutched fan, because you think it sucks horsepower, fogedabowd it. In the first place, the fan only works at lower speeds, and even in full-on mode, and in Drive I doubt that you'll ever feel it cut in. Secondly at WOT, and over 35mph, the darn thing is mostly freewheeling with the Ram-Air that is slamming thru the rad. It's a non-issue. Once your system is able to over-cool, the T-clutched fan will take care of business, alowing the stat to do it's business.