Re: Pusher Fan
While you may have flushed out your radiator, it may still be corroded inside, especially if it is very old and the coolant has not been maintained properly over its lifetime (who knows what former owners did). Brad is spot on concerning the aluminum radiator. My engine is 11:1 and after I changed to an aluminum radiator, no more overheating. As for the thermal fan clutch, others on this forum have mentioned issues with heavy duty fan clutches, so you might want to go with the standard model if you elect to replace it. Pusher fans are not as efficient at moving air as a puller, especially if you are trying to push through an A/C condenser first and as mentioned above, the pusher will partially block the condenser/radiator which may further exacerbate your problem.
Here is another thought. Is your vacuum advance connected to ported vacuum on your carb? If so, moving the connection to a full manifold vacuum source should be done for many reasons (you can find those on this forum) one of which is cooler running engine at idle. If you do this, you'll want to check/reset your base and total timing advance to make sure they are still within your desired limits. Your car will also run much better with this change.
One other thing you may want to check if all else fails and that is the condition of your water pump impeller. For various reasons, if in really poor shape the blades of the impeller can be nearly completely gone and the pump will not move the coolant through the system as necessary and the engine will overheat.
'69 Z/28, Lemans Blue/White Stripes, DZ302, Tremec Magnum, 4.10, Procar Elite Seats,
Custom Upholstery, Dynatech headers, 17" VWW V45's, 235/45, 275/40, C5 Front Brakes