Difference between 73-76 stepside box and 77-87 stepside box HELP!!

[80heavychevy]

So i am asking to see if anyone can tell me the difference between the two? lights, bumpers, dimensions, anything! ect. For my build (1980) of course it would be ideal to go with a 1980 box, but i am curious as to what they both entail in terms of differences.

any information would be much appreciated!

[Captkaos]

The actual box (sides, front, tailgate, crosssills steps are identical.
The difference in the 73-78 (note range) and the 79-87 fenders is the gas tank opening style.  73-78 had a round hole, 79-87 had a square door.

[80heavychevy]

Okay thanks, this makes things a whole lot easier!

[kcwis]

The second from front mounting bolt holes are in a different location , other than fuel doors is anything else different?

[Peter S]

The 78 & down fenders had side marker lights, 79 & up had the side marker light incorporated into the tail lights.

[kcwis]

I should have posted that the 82-76 box swap is fleetside,sorry