What you need:
4x LM8UU linear bearing (or similar)
6x M3x25 or M3x30 screw (longer works too)
4x M3 nut
1x M10 or 1/8" pneumatic fitting for the bowden tube
4x Belt attaching clip (from previous carriage)

There aren't many lightweight bowden carriages for J-Head on Prusa and the ones I tried weren't as sturdy as I needed. So the logical thing was to design my own carriage and share it here. I have now printed almost 1kg of material with this and I am loving it!

It uses four LM8UU bearings that snap in place. You may use zip ties if needed, I didn't. Hot end is fastened with two horizontal M3 screws through the groove and depending on the hotend the pneumatic fitting is either screwed to the hotend or the carriage. The result is a rock solid high performance carriage. Belt attaching holes are spaced 10x20mm, like used in most carriages. If you need a different type belt mount just let me know and I'll design it for you.

Update!
I received my authentic J-Heads (they beat all the clones btw) and found out they use M8 hollow screws instead of M10 like the ones on ebay. Pneumatic fittings with M8 thread are hard to find so I altered the design so that the M10 fitting is now threaded to the carriage rather than the hotend. I also added M3 nut traps for the belt.