And one more, this is my modification of an Athearn Blue Box kit. Although the metal clips and draft boxes work okay, I prefer the Kadee draft boxes. Instead of building the car as per instructions, I put the underframe upside down in the car. Since I don't open the doors of my boxcars, having the "wood" floor inside doesn't matter. I prefer the "wood" side down.
First, cut off the tabs that hold the underframe to the car body, these are the approx 1" long tabs on each side where the doors will be. Next, cut the draft boxes off the undercarriage. Drill and tap the holes for the truck screws, then glue the undercarriage onto the upside down floor, using the truck screws for alignment. Use clothes pins to hold it together while the glue dries. Glue some plastic strip above where the couplers will go.
After the glue is dried, use a Kaddee draft box lid to determine where the holes should be, and drill and tap them. Remember that the draft box needs to stick out a ways past the undercarriage so they will clear the body. Play around with the body/coupler/undercarriage to get it right before drilling. Also, you may need to file the car body just above the draft boxes, you don't want the body forcing the draft box down. This is true of any of the above types of cars.
My experience is that this modification of the Athearn doesn't require any shimming for a #5. You may need to file the floor under the draft box at an angle to correct any "hanging down at an angle" of the coupler. In other words, sometimes the coupler hangs down and is not parallel to horizontal. This can be corrected by shimming under the back of the coupler box or by some filing. This also holds true of any type of car.
Finally, replace the wheelsets with Intermountain or Proto2K, attach the coupler box and the trucks and add weight and you are done.
One last thing, as I mentioned, I don't like the steel weights because of possible reactions with the uncoupling magnets. Flattened fishing weights could work, maybe lead can be gotten at a plumbing supply, or you can buy lead roof jacks at the hardware store. These are pretty expensive, but they are made out of sheet lead and you can use these to weight gondolas and flat cars. This stuff is real easy to cut and work with, it can be cut with a hobby knife. Don't forget to wash your hands well after handling the lead.
Oops, one very last thing... since we had to cut the tabs off the sides of the floor (because they don't fit right since the floor is upside down), we need to use some white glue in several places to hold the floor to the car body. You could use plastic cement, but then it would be difficult to take it apart if you ever needed to.
