Just starting to build up my tracker. I have replaced the rocker panels with the 2X4 rectangle tubing, and repainted whole car, so had to replace the Plastic Bumpers. I used 7' 2"X4"X1/8" and 2"X2"X1/8" rectangle tubing on rear bumper.
First, I notched the 2X4 tubing 2" down and 1" deep matched to the bumper mounts (and same width) in order to recess the new mounts and allow the new bumper to fit tight to rear of body, instead of sticking out like the old bumper did. I then welded some scrap material I had into the cutouts to make new mounts for bumper and to keep the bumper sealed. You could reuse the pieces cut outs by flipping them over and welding them back into position. I recommend drilling holes into new mount pads before welding them into bumper in order to make sure the holes match up with the frame. The center mount cutout has to be much wider than the mounting pad or else it rubs on tubing on each side of the mount pad. I got to involved in making a tight fit on my mount, next time I would just make it 13" long, much faster/easier, and its under the bumper, no one will see it.
In order to follow the existing body lines I then notched the front side of bumper at the inside of taillights on each side in order to bend bumper. I then notched the front side of bumper again at outside of body to make it wrap around body. My measurements were a little tight, so had to cut out the top inside of the wrap around section in order to keep it from rubbing on body.
Fit up was good, so I drilled mount holes through top from the bottom up using the existing holes. These has to be angled slightly as the frame mount is not square/level with the world.
To finish things up I added the 2"X2" square tubing to top of the 2"X4" bumper to keep with the lines of the Tracker. Then I welded tabs to the bottom of bumper to connect to the bottom frame mounts and drilled to match existing mount holes. After capping the ends, (grinding and smoothing appropriate places) and painting I had a bumper that bolts on using all existing mounting positions.
Flush mounting brackets cut, checked for fit.
Works great, but would be easier to just cut out a 13" section instead.
Checked to make sure everything lines up. before cutting the corners.
Initial bend to fit the curve of the tail lights.
Cut and bent for the corner.
Hanging by the bottom mounts for painting.
Finished product mounted on the Tracker