Jack,
one very common problem with rear engine cooling systems is STEAM.
If the cooling system builds steam,it will develop air pockets and seriously hinder circualtion.
Here are some basic tips:
#1:make sure that your filler cap is at the highest point in the cooling system.
#2: put an "air bleed" on the highest point possible on the radiator.
Run a hose from this air bleed to the surge tank. This will allow trapped air to "bleed" to the top of the system, which will help insure good flow of coolant.
#3 STEAM- air bubbles are usually cause by steam in the system ( or exhaust gasses entering the cooling system via leaky head gaskets)
One way to control steam is by adding a restrictor at the entrance of the radiator.
A washer with a 3/4 inch ID hole works for most V8 engines.
The reason for doing this is to allow the water pump to "pressurize" the line going into the radiator, so that superheated coolant will not "steam" until it actually reaches the radiator,,,where it can condense back into liquid.
#4 airflow,the key to airflow through the radiator is not to have a huge hole in front of it,,,,,but rather to have good ducting which will not allow air to bypass/or bleed around the radiator. Aluminum, rubber, etc can be used to properly duct your radiator.
Also, the area behind the radiator is also critical for good airflow.
For times when you are not moving, you want a good pair of electric fans mounted very close to the rad fins. Most elec fans are designed to be within millimeters of the radiator in order to perform properly.
I find it is best to have any temp sensor for the fans mounted on the cylinder head for accurate activation of the fans.
#5 thermostats, some will tell you that they run without a thermostat. I do not agree with this philosophy. You need a thermostat to control the system, and also a high quality rad cap. A higher pressure read cap will also raise the boiling point of a cooling system.
One inexpensive car which can be sourced is a 22psi unit for a mercedes 190 or 300e.
These are less expensive than buying so called "racing caps" and have a 22 psi rating.
Oh, my coolant of choice is distilled water and redline "water wetter, with pump lubricant".
Of course this offers no freezing protection, so that must be considered for those in colder climates.
I hope this helps. Alain