I've installed 2002 Silverado Seats into my K5 Blazer. After doing that I don't belive that they can be installed into a standard cab 73-87 truck without some major re-engineering.
The main difference is the floor height. The K5's floor is flat (even with the front section) under the seat. The standard cab trucks have the hump in the floor for the fuel tanks. The Silverado seats have a 6-7" tall seat track/mounting system. This is why when I installed mine they came out at the right level (see attached pic). However, this seat track mounting system would make the seat sit that much higher over the hump in the floor on a regular cab truck.
I've looked my seats over pretty well and the seat track setup does not look to be removeable from the rest of the seat frame. It's all pretty beefy under there. My only thought for this setup is that since the seat itself contains all three seat belt attachment points and anchors the seat to the floor it has to be beefy and built as an integrated unit.
My dad had bought a pair to convert hit 02 silverado from manual to power and the seats we found came from a rollover. Turns out it must have been a big dude in the seat when it flipped because the sheetmetal pan that the foam sits on was torn in 2 spots and the lower frame was tweaked. (wouldn't sit flat). He had the local dealer look it up and the only way to fix what was tweaked was to buy the entire lower half of the seat minus foam and uhpolstery. In other words, GM don't sell the seat tracks separatly.
If you have a Crew Cab truck, Suburban or K5, the Silverado seats are almost a bolt in deal. I just had to make some brackets to bolt the tracks to and then to the stock holes in the floor. Installing them in a regular cab truck is going to take some effort. If one was to do it, you have to make what ever you do very strong as to take the forces of a crash with the seat belts on the seat itself.
