Or is it because they made 73-79's much longer and while the 83-86's were made slightly longer they are also newer and not as many have been lost to attrition? They are all very few and far between around here anymore and 3/4 of them look sketchier than Rusty #1.
Dad's '80 F-350 was a tank. It was a go anywhere do anything truck. I know dad overloaded it with the gooseneck hauling tractors, it hauled hay... if it fit it shipped. When he cleaned all the tools out of it to sell it the bed floor was pretty much beat flat and dipped between every bed crossmember. It had a hoist in the back passenger side corner when not in gooseneck mode to lift whatever the ol' 400 could counterbalance, that thing was tested tough. 0 frame issues.
Only problems were a 4x4 hub, ignition modules (until he put a Ford one in it), the 400 would blow coolant like yours does, body rust and he would get about 100k out of an engine. It was in need of engine #3 when he got rid of it.
I was saying rather than spend $280+shipping on a shifter to fix a transmission, I would be tempted to just get an M5OD that uses a $15 shifter rebuild kit to fix the shifter.