Well, I have seen the photos and I see a very nice, white 73 in good form, obviously doted upon by your Father-in-law or previous owner. Photo labled "driver side hose" This is (was) the vacuum supply for the air injection system. Although we may argue on some items, we pretty much agree that the air system does far more harm than good. keep it pluged, or consider removing the rest of the system entirely. Photo Labled "lower hose" this is the crankcase vent that was connected to the PCV valve on the original setup. Do not plug. All engines need a crankcase vent, for more, the merrier. Before the mid 1960's, engines were vented to the atmospere, via a "draft tube". This is in no way "eco-friendly". Many here, who have fitted an alternate carburation system, have installed a "puke can" (lovely terminology, I perfer "catch can") to connect this hose, and the valve cover vent hose (below), to keep them vented, and keep the oil off the street. Photo Labled "valvecoverhose" see above. or just fit a small filter, availible in most Hot Rod shops, From K&N filters, to both hoses.