This would be a true case of 'extreme measures'. The powerful local signals from across the river are going to make reception from 70+ miles very difficult (I'm trying to be optimistic).
It looks like every signal from Philly will be facing both co-channel and adjacent-channel interference.
You would very likely need to build a custom antenna for each channel received. Each antenna would be required to have very high gain in the desired direction while also having deep nulls in the direction of stations on the same frequency.
Of course, you can try a big antenna such as the Winegard HD7698P or Antennacraft HBU-55. (If it fails to give the desired results, there's ebay & craigs list).