I have done this swap. You can transfer all of your Viper skid pieces to the 136" rails. The front arm will still bolt to the original mounts in the tunnel. The rear and center mounting points in the tunnel will need to be moved 7.5 inches back from the short track mounting position. you will need to use 97-99 mountain max/venture/phazer mtn lite rear drop bracket's, rear outer tunnel braces, (used for rear drop bracket mounting bolts).
For the center mount inner tunnel brace, you can either relocate the stock short track brace, and grind approx 1/8" off the heat exchanger vertical ridge. Or use Mountain Max center mount braces
The rear mount cross shaft and outer spacer sleeve's will either need to be shortened, or use a mountain max shaft and spacer's. This is because the MM rear drop brackets step in from the tunnel. The Viper cross shaft (aluminum) is lighter then the MM shaft (steel). So I had the Viper shaft and spacer's shortened at a local machine shop.
If you look at the on line part's fiche for a 97-99 mountain max, you can see the bracket's, etc that I am refering to.