[1976gmc20]

Congratulations!

I think I had those exact same running boards on my 1991. They are sitting in the junk pile now after I finally got disgusted enough with them to fight all those little rusted bolts to get them off. It looks more like a real 4x4 without them but I did keep the little flap on the front to protect the rocker and lower door area.

From the lack of front hubs I'd say you have the NP203 "full time" transfer case. You probably want to start working on a plan to convert to NP205 (or NP208?) part time, and add some hubs.

As far as tires and wheels, I would highly suggest spending the money for some new 16" steel wheels, so that you can run a load range E tire. These things are heavy and eat 15" tires if you get off of pavement. I searched all over for used 16" 6-hole wheels to fit and struck out. I finally ended up with some 15x8 rallies but still the same damn problem with tires. Just so you know, the 16" 6-hole GMT400 wheels Do Not Fit because of the backspace.

Anyway, these are just incredible vehicles. Your 1978 looks better than my 1991, but other than the color and grill they look almost alike.