The problem I have with the Facebook instructions is that it requires filing of the needle bar which permanently alters it so you can't revert back to 15x1 needles if desired. According to comments made by Darren B in this thread:
it sounds like you don't need to file the needle bar and permanently alter it. The round shank industrial needles are held adequately without any permanent modification of the needle bar and all you have to do is loosen the three bolts on the bottom of the arm's casting and move the bed roughly 0.015" to the left to accommodate the new position of the industrial needles. I did pick up from the Facebook group's needle modifications file though that 134x5 and 135x5 class needles are the easiest choice since they're the same length as the 15x1 needles and don't require changing the height of the needle bar. I'm guessing that if you're sewing really thick material / leather you go to the 135x16 / 135x17 needle system since they're about 1/8" longer and I think those come in larger sizes to accommodate even heavier thread. I had hoped to see if anyone here besides Darren had done this and what their experience had been.
Just for purposes of keeping all the information together for future reference. 134x5 is also known as 134D, 135×7, 135×25, 1901, DPx5, and DPx7 according to http://southstarsupply.com/product/schmetz-needles-134r-135x5-135x7/ It's a confusing system. 134x5 needles are available in both sharp point and leather point although leather point needles seem to be less common in this system. I'm not sure how 135x5 needles are different from 134x5 needles. The 135x16 are leather point needles and 135x17 are sharp point needles for fabric.