Well, there was a factory option to have a second battery on the driver's side, so if you have only the one battery, that tray set up is basically a bolt-in affair.
On my '90 3/4 ton /forums/images/graemlins/burb.gif I had to move a charcoal cannister or something, and drill maybe one hole. On the '74 /forums/images/graemlins/k5.gif I think I had to drill two holes, and move the horn... all pretty easy hand-tool stuff.
LMC carries them, either a genuine GM part or a repro, anyway, as the one I bought from them had a GM sticker with part #.
The dealer also carries them, though pricing will vary. I seem to remember paying maybe $50 for the bits I needed for my '74, back when I didn't know about LMC.
The LMC catalog is helpful as it shows you all the pieces you need -- I forget with these newfangled trucks, but they're different from the 73-80's.
Now, the military diesels I've seen (donno if this is also available on the civvy) are psuedo-24V, so they have a different dual-battery tray, that holds two together, on the passenger side of the vehicle. I don't know if one of these would fit in a gasser -- though I've always wanted to get one, the two batteries I have in my trucks do me just fine /forums/images/graemlins/laugh.gif
You might be able to get one from somebody parting a CUCV, fwiw.
HTH. If I completely missed the quesiton, apologies, and if you want, I have pix of all of these setups above.
-- A