When it showed up on my porch, it was a bit disconcerting, as it appeared to be a return (also had a Ford bolt set in the box. After some happy thoughts, I assembled my tools (including Liquid Wrench, you may choose your own) and unrolled a few rugs on the ground underneath the back end.
Tools you will want: a 3/4 inch, a 15mm socket and 16mm socket. Don't know why the metric stock fasteners and the new hardware are different, but arguing with a van is a sign of advancing age... Possibly due to a higher grade of fasteners....
A 3/8 inch drive, with 3" and 6" extensions.
A 3/4 inch, 15mm, and a 16mm open end box wrenches.
A torque wrench, capable of 38 and 75 ft-pounds. A beam wrench will work, but it will demand a bit of repositioning. A click wrench would be good, except the arrangement of the bolt heads going into the bumper and the one that goes up under the rear door sill makes for a darned tight squeeze.
You may want to drop the spare, I didn't, a little cramped toward the driver's side, but not bad (I have the doughnut spare).
For extra credit - a 1/2 inch drive ratchet.
For extra credit - a 1/2 inch breaker bar to ease things free....
If you have somewhat rusted frame nuts on the forward frame, the new 10mm x 1.50 bolts will not even start (nor will the original bolts!). You could use a tap to gingerly clean the threads in the forward two frame nuts.
To make dropping the original bumper brackets easier, leave one loosened bolt at the front of each bumper bracket to hold the bracket while removing the last rear bolts from the bumper, otherwise it wants to twist on the bolt as you remove it...
Once you remove the bumper brackets, don't despair if the holes on the Valley end brackets appear not to align front to back. There is a single, 10mm bolt at either end of the bumper, loosen them so the bumper now pivots on that bolt. NOTE: Valley asks you NOT to put any load or weight on the bumper when it is loose like this...
Grab each end bracket, and start the new 10mm bolts. The Valley pdf sorts disappoints, the correct assembly order for the frame bolts are bolt, split washer, then flat washer. The only place that does not use the flat washer is the 10mm bolt below the rear door sill (passes through the reinforced tab).
Now balance the tube on your stomach, line up one end, start a bolt, move to the other end, start a bolt. Now it's easy.... Once everything is snugged up, whip out the torque wrench and starting on one end of the bracket, start torquing all 10mm bolts to 38 ft-pounds. The bumper bolts are a little fiddley, but it is what it is. The Valley end brackets use a 3/4 inch bolt head on the 1/2 inch bolt, torque 1/2 inch bolts to 75 ft-lbs.
Note: I have seen where you would want to keep a torque wrench operation in roughly the middle of the range, so the maximum 75 ft-lb torque wrench really should have been 100-125 ft-lbs...
This is the old bracket snuggled up to the new Valley bracket. Note the arrangements of the yellow zinc chromate bolts.
This shows how little of the 73640 receiver is visible after installation:
