I have a 91 suburban console in my 78 C20.
Here's how I added front cupholders to it using one of those cupholder units thats supposed to go between the console and the seat in normal cars.
I was working out of my truck doing framing and trim when I added this. I needed more space for stuff.
Ugly from the bottom but nobody will ever see that.
From the top I filed it down to fit the console. It takes a while but the result is worth it.
Use 4 bolts to put it together with the stock 91 console.