If you are talking about a street car and you don't want to impacts the looks when you occasionally run up to triple digits, there is nothing you can do, unelss you are willing to sell your 70 and pick up a 72-74 with a more flush mounted grill already present.

If you are running track days where you don't mind a specific modification that can be reversed for the street, some sort of frame the fills the surround, can bolt to existing hardware, and has screen door screen stretched tightly over it can actually do a lot for pushing the built up pile of air around the nose instead of allow it all to go through. The mesh does allow enough airflow for the radiator, but acts similar to a small sink strainer when excess air is pushed against it.