OK here is the original thread that I had started.
1. I removed the milk jugs, tow hooks, and bumper pads from the original TJ bumper.
2. I cut 8.5" off both sides of the bumper to allow the JK bumper to slide over the original bumber. Make sure to measure from the front as that is the longest point. If I recall correctly you want a total of 37" left of the TJ bumper.
3. After that I just used a piece of cardboard and pushed it down on the bolts of the JK bumper to get the imprints and then drilled the holes in the cardboard to use as a template for drilling the holes into the TJ bumper. I used a 1/2" drill bit because that was the larget I had. I did have to woller the holes out a little so I would recommend going a little bigger if you have the bits available. Going off my memory the bolts were 3.5" apart (left to right) and 2 1/4" apart (top to bottom). May want to measure that though.
4. I removed the bumper cover from the JK bumper, and also drilled holes in the top and bottom of the JK bumper to line up with the original mounting holes of the TJ bumper.
5. Along the bottom lip of the JK bumper you will need to either bend down or cut a notch (in the lip only) at the point where the steering gear box is. I just bent mine down as I did not have the saw with me when I was doing this step.
6. Once all this is done, I put the TJ bumper inside the JK bumper and bolted the two of them together. I believe the nuts I used were M12x1.5 and also flat washers because I used nylon self locking nuts.
7. Take the two bumpers assembled together and mount to your jeep using the original TJ bumper mounting holes. You can add some spacers to avoid doing what I did which was just closing the gap between the JK bumper and the TJ bumper using the bolt and running it down (The cover will hide which ever you choose to do).
8. Once the bumpers are bolted on, you are now ready to put the cover on. In the two holes for the tow hooks you will need to make the notch a little bigger. Going towards the back of the JK bumper I just used the knife on a Gerber multitool, and cut the notches back about another 1/4" or so. This will allow you to be able to slip the cover on. It does take a little bit of persuasion though. LOL Once the cover is on then you just use the 4 bolts that hold the cover to the bumper to secure it. These four bolts can be easily accessed with everything on.
Total project after getting the JK bumper for free and selling my stock TJ tow hooks for $20 and buying the locking nuts and washers I came out about $10 in profit. Not a bad upgrade to say the least. LOL