Lemme guess, the impala has those 5 3/4" sealed beams... the high beams have two prongs on the back, and the lows are a dual beam with 3 prongs on the back? Bosch and Hella make a conversion for the 5 3/4" sealed beams that convert the lense to a nice flat glass lense, and then you can put a H4 bulb of any kind, and it uses the factory connection. I totally see where you're coming from with doing the Angel Eyes conversion... I keep telling my buddies with their 66' Lincoln Continental and 64 Ford Galaxie 500 to do the same conversion that you want to do. But yes, the angel eye conversion is a 5 3/4", just like the sealed beams you have. PLEASE show me a pic of what it looks like when you're done!