Round hole to Squaer hole.....

[THE "10" SILVERADO]

I have been contemplating switching my 77 passenger round hole quarter panel for the newer (79-80?) panel with a square fuel hole with the door to it....does anyone have anymore information about that? was the square fuel hole w/ door an extra option? and what would you have to do to switch? is the fuel neck different? I know this is kinda a lot but I want to head to a junkyard soon to do the swap before I prime the truck and need to know how to get the new panel off (it's just bolted on right?) and get it on me truck if you know anything about this or could tell me what to do that'd be really great!!!

Thanks!!