ok, here's some info for you low-fuel relay gurus. The 72' parts book shows the low fuel relay as being a 2983828 the same I guess as used on the previous Gran Coupes and SE Challys. However, that part number changed after Nov 1971 to 3620858, 3620859, and 3620860 depending on the model car it was in. The bracket is in different locations and the 72 unit only has three posts. I think they did away with the separate ground post and use the bracket-to- body as ground.
The good news is that there are a few of these units still in stock at Ma Mopar. Also found the time delay relay 2889565 for the seat belts (same as the 70-71 SE and GC). Got both of these for under $20 shipped.
Sure beats dealer pricing and shopping here: