I see 100 as the average running temp in mine. Been in the high 90's with hugh humidity here in GA. Yes, your screaming at 75... there is always the option of tossing in a later rear end... (I have one out of an 83 I thought about putting in mine). I don't thing it would do the car any favors as far as it being able to climb hills so I have not done it.

SAve yourself some grief and just go ahead and remove the radiator from the car and clean it. You'll be shocked at the amount of crap between the 2 even after you have "cleaned" it the other way. Besides, it will give you a good reason to go ahead and replace the hoses too...