Nerf bars won't cover up the gap, since they are at the level of the frame, not to mention you won't find nerf bars for the pickups due to the side tanks.
Lift Lips is a company who makes cover ups for the unsightly gaps.
I personally do not like body lifts, but if you do, here goes:
It is not that difficult to do. You will need a helper, to help lift the body one side at a time. An impact wrench will speed things up. No special tools are needed. Just sockets.
One exception. With an automatic transmission, you need to lengthen the shifter linkage the same length as the amount of body lift. Either weld in the extension or figure out a way to use threads. Welding is simplest.
'79 GMC shortbed 454 th400 14 bolt FF NP205 Dana 60