I had an 85 T-Bird which is pretty much the same car as your Cougar.
If you live in an area where the road crews use salt in the winter expect the top of the
gas tank to rust and perforate. DO you smell any gas when you fill it up ?
The fuel pump filter assembly is held in the top of the tank by a ring that gets very
rusty. Once you take an original pump out expect to replace the entire assembly including
a new locking ring and maybe a new tank as well. Accurate fuel gauge readings are hampered
by poor electrical grounds and the use of a marginally working voltage regulator attached
to the back of the instrument cluster. As these cheap regulators age they don't provide
the proper voltage to the gauges (think it was 7.5 volts) causing all kinds of misleading
things to happen to the analog gauges. You won't see this if you have the full digital
dash. The cluster is a real pain to take out from what I remember. In 230,000 miles I had
the cluster out at least three times for replacing the halogen lamps for the LCD speedo
display and once removed the entire dash to replace the heater core. One of the ugliest
jobs I've ever attacked.