Nospark
If the radiator fan was running all the time, that was probably your biggest issue as far as warm up. On a 6/1, anything much larger than a metro rad is overkill, so in 20F air, even a little airflow can dissipate way more than the 17KBTU/hr that the engine can put into the cooling system at full load. Basically, like hooking it up to a swimming pool sized cooling tank, you gave it a nearly inexhaustable supply of very cold water from the bottom of the radiator. You could also run into this situation with a metro radiator and a good flow of 20F air. The 180F thermo probably is still cycling also, but with the slightly lower opening temp and a bleed hole to allow constant flow, I am sure the swings are not as extreme. Big semi trucks also run into this problem in winter. They have a simple solution. They put a cloth cover over the radiator inlet with a zipper on it to block a great deal of the airflow from the front of the radiator. They unzip this cover as neded to control the airflow and match the radiators cooling ability to the engine output.
Personally I would put the 195 thermostat back in with an even larger bleed hole. I bet it will work just as well in dealing with the swings as the 180 has. The biggest fix though will be to get that fan control working so the fan dosn't run untill the system is warm, and can shut off so it dosn't remove too much heat from the coolant. The thermal switch controlling the fan can also give you an idea of how well the cooling capacity is matched to the heat load. If the fan switches on and off at a fairly fast rate, it is moving too much air and overcooling the rad which causes the short cycling. If it comes on and stays on all the time, it is probably not moving quite enough air. Observing the fan cycling as well as the temps around the system will help you to match the cooling system to the engine. IMO, ideally, you would want the fan to just stay on all the time at maximum load, and occasionally cycle off, say staying on 90% of the time at lesser loads. In winter, use something to block airflow thru the radiator to maintain theis same relationship in the much cooler air. Your goal is to be able to remove enough heat that the cooling capacity is within the thermostats ability to control without fully opening or fully closing. You might find a much smaller fan or two, such as a 4" computer case box fan setting on the radiator face, can move enough air to maintain control.
Another good reason for the 195 thermostat is combustion efficiency. That 180F thrmo limits the upper operating temp. I noticed a significant difference between a warm engine and a cooler one during my fuel consumption testing. It does make a difference in how much fuel you will burn, and hotter(below boiling) is better IMO. This may also make a difference when running alternative fuels as it will probably cut down on carbon buildup from the heavier oils.
Good luck.