Those in the Midwest probably remember the Williamson 5 in 1 units. At least if they've installed or removed one, their backs still do
Here's one we pulled out. The 5 in 1 had heat, built in coil, built in EAC & hum. We replaced with a 2 stage 80, no way to vent a 90. Had to reset the coil in the plenum and install a hum. Took 3 guys all day. Lots of metal!