My timing is set at 17* using an adjustable timing light.  I use full manifold vacuum, not ported or the TCS solenoid.  Factory says 4*.  Definitely try advancing your timing.  Drive it, if it pings on hard acceleration, back it off a bit and test again.

13" Electric fan is mounted on the front as a supplemental to the OE mechanical in the rear. With anything thicker than a 1.5" core pushers are more effective at passing air through all that resistance.
Timing with a light is at 14 degrees. But I'll read up on the vac system of timing. If I build an engine I'll typically put a degree wheel on it and timing tape the balancer. 
I'm starting a new thread with pics of the rad. I think its the wrong model.

Joel be the man!!!!   I have set timing solely by Vacuum and use the timing light only to get a "ball park" reading. If you set timing with a vacuum gauge you would be more accurate along with being sure your valves are opening and closing correct.If you get a "bouncy" needle you have a incorrect valve or adjustment,just be sure to have your vac advanced is closed off and you are connected to straight vacuum source,i.e. intake manifold vac or at least straight off the carb(UN METERED PORT).You will advance timing while increasing vacuum from what you have now ( abase number i.e.10 inch hg.)to a larger number.If you have a big cam you may not get more than 12 -15 hg. and if you can get to 16-17 in.hg. you are looking good,however you should have to decrease your throttle linkage (idle screw) to your desired idle RPM.Once you have your curb idle down where you want it then reconnect vacuum advance line.       

On the heating problem;  I had the same scenario with my '80 and subsequently had to take it out and have it severely cleaned and have not had a problem since.It seems as it sits around it precipitates the inorganic solids i.e. Ca,Mg,etc and reduces the available resident time for the water to allow it to cool properly. Also when I refilled my radiator/engine I filled with distilled water,ran the engine for 10-15 minutes to be sure all the "hose" water was gone,drained and added desired coolant to radiator until full,installed 16 lb. cap to radiator started it up and idled for 15-20 minutes allowed it to cool until next morning with the cap just sitting on opening of radiator to allow any air bubble to escape overnight then top off radiator and the check next two days to see if will take more coolant,assuming you don't have a leak.As you can tell by this manuscript I have done this a few times in my life..Take car and good to great luck.