I followed this build and bought from Marlin, too. I decided to make mine bolt-on and used a u-bolt design using George's drawings at the frame mounts. Worked out very well. I was able to use the 12" legs included for 4 of the mounts (trimmed to fit), the front ones are much longer. To go under the cat, I used round tube, but in 2 pieces welded to a 1/2" barstock directly under/between the cats so it wouldn't go any lower than the cat. From this would be easy to build a cat skid similar to the metal tech sliders, but I haven't done it yet. I also trimmed the pinch weld to put the sliders as high as possible. In doing so, I had to notch and reweld the middle leg at an angle to clear everything. I didn't use the included gussets as they are pretty tiny. I made my own from 1/8" flatbar to extend more of the length of each leg, as those long front legs seemed like it could flex a bunch and I don't have much tolerance for flex with the pinch weld gone. They got a couple scrapes at CM, but I found all the other stuff underneath was likely to drag first. Didn't lay on them hard to see how much they move yet.
Good luck on yours and thanks for the idea Box Rocket!
Any Pics?
And whats George's drawing?