Never noticed? but thats one of the main features of the 707
What yu mean "pylon" are actually turbocompressors fitted on three of the engines, to provide extra air for cabin pressure, air conditioner and bleed air to engines. The engine nr 1 didnt have a turbocompressor.

Neither any of the 4 engines of the DC8...for example.

The turbocompresor is a main exclusive 707 feature.