Side steps/nerf bar steps

[rgunlock]

Need some help on ideas for fabricating a rear mount for nerf bars to go on a 78 GMC K15. This truck has saddle mount gas tanks. Got some universal nerf bar/steps from Dee Zee that were supposed to fit my truck. They state that some fabrication may be needed, but the mounts that shipped don't even come close. I haven't found any others more specific to this model truck. In order to get the step low enough to clear the gas tank, I only have two bolt holes into the frame up front, and as you can see from the picture, the rear mount will be 9-10 inches below the frame due to the step up in the frame.

I've done the google search on this site and in general and I'm not coming up with any good solutions. I'm not sold on these particular nerf bars even though I bought them, so alternative ideas would be appreciated. I don't think that the little steps that screw into the inner rocker will support my weight for long, so I need something frame mounted that can deal with my saddle tanks that cover the frame halfway up the cab. I can weld well enough, so pictures of how you've dealt with this will be a huge help.