Rob... I did this to mine and used a couple pieces of smaller square tubing. It was either 1" or 1 1/4" square tubing, I don't remember which. I just cut them as long as the original mount. Painted them, drilled the holes to match the holes in the floorboards & frame (they go inbetween the frame & boards)& used grade 8 bolts & locktite to button it all back up.
Works great & gives you a little more room. I also cut down my brake pedal for more foot room. If you want pic's let me know & I can take some & see if I can figure out how to post them.