i just mounted up a nbs on my obs tonight, took me a couple hours, posted on facebook and heard you are having problems? its VERY easy! wish i woulda took pictures to show you better, but i will explain my best!
1) Take your OBS bumper brackets off your OBS bumper.
2) Remove all brackets off NBS bumper. leave the two top bolts in the NBS bumper (you would have to take off the black black ontop of the bumper to get them out.)
3) Take your OBS bumper brackets and put them on your NBS. You will notice you can only get the bottom bolt in and it appears you would have to weld a tab to get the top bolt to work, WRONG! drill a hole on the top of the bracket for the top bolt to go into, I made mine oval because i just drilled a hole first and it wouldnt line up right on the truck. Drilling them oval will give you some side to side adjustment.
4)Once you have done that on both mounts, put your mounts on your NBS bumper and tighten then two bolts up on both sides, I left mine loose so i could adjust if needed.
5) Slap the NBS bumper on and bolt back into stock location. (2 bolts on each side) You may have to oval out those holes too because currently my bumper is tilted up a bit, I havent taken the time to mess around with it yet. Also you will notice it hits a bracket off the frame cause it to be tilted a bit so you will probably have to do some trimming.
If there is anything you dont understand I can get some pictures for you, or answer any questions.
Also, I took off my OBS licence plate lights and put them in my NBS bumper, they fit perfectly. I just added in a little wire because like you said, they are too short. Here is my finished product after ~2 hours of work.
Once I got one side figured it out, it probably took 10 minutes to do the other side. You may also want to over size the bottom bracket mount a bit to give you some adjustment
