I think you are getting confused.......the fan, even a stock/ aftermarket fan at 2800rpms is accelerating the air flow through the radiator, not slowing it down. Especially in combo with a shroud, this helps direct air where it needs to go.

I believe we have officially killed this thread! Sorry OP.

You are OBVIOUSLY uNinformed ...

...and to add ... adding a typical old-school shroud into the combo ...can actually RESTRICT the flow even more ...

I have to agree with Doc this time. At speeds above say 30 mph the is not needed for cooling and can in fact somewhat restrict air flow. Don't try city or stop and go driving without one though.

Is there a heat gage that can be purchased "off the shelf" that will work with the stock Chrysler "heat gage sending unit" that is in the engine?

You might benefit from going to Harbor Freight and buying a "Non-Contact Laser Thermometer". That way you can just point a shoot to get a temperature reading.

I typically shoot the top tank, bottom tank and Water Pump housing.

Look for the delta T across the radiator top to bottom. The more temperature differential across the radiator top to bottom (within reason) the better. I sometimes pull the radiator cap while it is running and shoot the actual liquid, but it is usually the same as the top tank.

This generally eliminates the inaccuracys of the gauge and you only have to deal with what ever the accuracy of the Laser Thermometer is. Mine is a Cen-Tec unit that works pretty well for the price, but I am sure there are others.