flex fan

Yeah my 80Volare can barely keep itself warm on the hottest summer days,lol, even with the lamo 4blade fan, and an automatic. In winter I used to block the rad with cardboard, completely, and right tight to the fins. The only time it ever "over-heated",was cuz the top rad seam blew open, and she puked all her coolant out. That was a scary ride home 10 miles, putting more water in her every mile. Thank goodness for Ditch-water, and a spare ww jug!.
If you can get a stock slanty hot, I mean truly boiling the water, hot, in Montreal Canada, congradulations. What's your secret?

There are only two reasons for an engine to overheat; 1) it is creating excessive heat, or 2) it isn't shedding enough heat.
As to creating it, look to retarded timing, and lean running, and a plugged exhaust.
As to shedding the heat, look to water circulation first, then capacity.This means that the lower hose is not collapsing,is first,and then that the water pump is in fact moving water. After that, look to the rad not seeing airflow through it. Perhaps the fins are plugged with dirt or debris.Or if an a/c car check the condenser for blockage. Then finally check the wp drive ratio. The block being full of sludge on a slanty doesn't seem to be an issue; as long as the coolant can at least travel to the back. You can get an idea of the water circulation by; removing the thermostat and putting it back together,removing the cap, and then blipping the throttle, while having one eye on the lower radhose and the other on the fluid in the top of the rad. The lower hose must retain its shape,and not get sucked flat. The fluid level in the rad should drop as soon as the rpm starts to rise, and it should pop back up as soon as the Rs begin to fall.Then while idling, the fluid should be constantly moving. There should be no bubbles in it of any kind, and it should not begin to steam until around 180*,or more degrees. Go boil some water in an open pot on the stove. It doesn't move around much until the temp is too hot to put your hand into, and it doesn't begin to "smoke" until just before it boils.
Put a scrap of paper about 8x 10 in front of the rad (no A/C), with the engine idling (about600). The fan should immediately snap it up tight to the rad. Tear it in half, and move it around from place to place. It should be the same in a circle the size of the fan, with less towards the corners. Without a shroud, and with the hood open,the pull is less pronounced.
The flex-a-lite with the 6 metal blades did not cool my 360HO, at all. It worked on the slanty just fine. I threw it in the attic and lesson learned for me.
If the engine has a blown headgasket and is pumping compression out, then the remaining cylinders are gonna have to work harder to get the car moving. Extra work is extra heat. If it has blown out between two adjacent cylinders, this is serious pressure loss. But by now you would be on to something being wrong. Retarding timing is more insideous, in that, as it happens gradually, you might not notice until it is quite far out, and then you would be wondering why your engine is so lazy.With retarded timing the mixture may not finish burning in the chamber. This leads to the charge continuing to burn in the exhaust ports and exhaust manifold. And the fuel mileage takes a dump.
To much timing also creates heat, if she gets into detonation,both the power and the fuel mileage take a dump.
Taking the stat out, with no compensating restrictor is the wrong thing to do. In a DD the temp may not come up warm enough to drive away the moisture and acids that form inside the engine .This leads to accelerated wear, and eventual self-destruction, as the engine accumulates moisture and condenses it into water. Eventually this water finds its way into the oilpump on a cold start, and pretty soon the bearings get hammered out. Short trips under 20 minutes will accelerate this.
So, you need to get after this.
I suggest your first purchase be an IR gun, and start targeting everything to do with the cooling system. 205* at the stat house, or in the filler neck,is not too hot. I (me personally) would not run much under that, with perhaps 190 as the minimum.