there are a Lot of factors that control cooling effectivness
in answer to ?1] it might be slightly less restictive to have 2 5/8 " nipples on the water pump the but the heater core also has 2 different sizes so the gain would be between none - minimal
2] Vitually ever 70 I know of had the ridgid fan but the clutch is better technology & is far more effective so I use clutch& 6 or 7 blade fan on virtually any build.
the high flow water pumps can help but the reality is the thermostat should close & keep the water in the rad long enough to properly cool it then open & switch the coolant with the hot coolant in the block & close again so it allow a faster transfer time between cycles & could cool it slightly better
3] coolant additives tend to eliminate the bouindry layer of boiling gas between the coolant & the hot surface so the transfer of heat to the coolant is more effective .
There are many other factors to having efficent cooling , , having enough coolant volume , adding more cores to the rad , having the upper hose on the opposite side from the bottom hose helps , using a 180* T stat helps ,advancing the timing a few degrees up to 12-16 * at idle can make a huge difference , just make sure it doesn`t over advance above 3000 rpm , you want to keep around 38 * total , if the engine is runing lean it can increase the temp significantly .
So why does Penske Suck , he has helped some of the best drivers get their start , has been nothing but passionate about being involved in racing all of his life , he has been very successful in business & has moved a lot of his profits into supporting racing endevors ?