Rear wheel wells same as pickup?

[VictoriaHardware]

I want to widen the rear wheel wells in my Sub to get more tire clearance on the inboard side. I was going to split the well down the middle and weld another split well onto it. Once finished it would appear perfectly stock, just wider.

As long as I've been around these trucks I though I knew it all but I've found that not to be true since I found this site. Once again I assumed that the rear wheel wells were shared with the fleetside pickups. Now that I start looking close I see that is not 100% correct as they have different horizontal ribs in the inner vertical surface.

Has anyone had the two in their hand and compared them? Are there other differences? Do I have to get a Suburban/Panel well to do this?