Too many factors enter into this for me to be able to give you a direct answer. Among the variables are, what condition is the towing vehicle in? What was the towing capacity of the vehicle originally? What modifications have been made to the tow vehicle, such as lift kits? There is a chart that gives you tow capacities for a 78 Scout elsewhere in this FAQ. It would be a very good source of information. I would urge you to err on the side of discretion and avoid trying to tow too much too early.
WHAT DO I NEED IN ORDER TO TOW A TRAILER?
A ball fastened to a bumper should only be used a very light trailer (maybe 500 lbs loaded). To tow any major weight you will need a towing hitch fastened to the frame. These come in a variety of capacities and you should decide what capacity you need, or if you already have a hitch, you need to determine what its carrying capacity is. All of these ready made frame-mounted hitches come with a socket called a receiver that accepts the piece of tubing that actually has the ball mounted on it. The choice of balls is as follows:
1 7/8" diameter for very light towing
2" diameter for medium duty towing
2 5/16 diameter for heavy duty towing
Most modern tandem axle trailers use the 2 5/16" ball.
In order to tow much weight at all, you will need to be able to use the trailer's built in brakes, and in most cases, this requires an electrical control to be added to the cab of the tow vehicle. This device, that can be activated either manually or by depressing the tow vehicle's brake pedal, applys the trailer's electrically activated brakes. In my opinion, we IHC owners are fortunate in that we can use the brake controllers that are activated by brake fluid pressure from the brake lines, rather than having to use one of the electronic models which tend to be much less consistent.
HOOKING UP THE TRAILER
What you hope to have happen when you are through hooking up is to have both the trailer and the tow vehicle level and looking as if the trailer wasn't putting a big load on the rear of the tow vehicle. In order to do this, an equalizer hitch is going to be necessary if the tongue weight of the trailer is more than a few hundred pounds. Note that if the tongue weight is very light, you will be in a dangerous situation when towing, so there is more to this than just weight distribution in the trailer.
Prior to actually hooking up, you need to level the trailer, and back the tow vehicle up to where you can observe the relationship between the coupler on the trailer and the receiver on the hitch. Your ball is going to need to fit up into the socket, and the tubing it is attached to is going to need to go into the receiver so that the levelness of the trailer and the tow vehicle is maintained when each is supporting its own weight.
This pretty much requires a custom "stinger" for each application. "Stinger" is one name for the piece of tubing that goes into the receiver and has the ball fastened to it.
So you've got the parts matched so that both vehicles are level when they are supporting their own weight and the trailer is fastened to the ball. Now you remove the support for the trailer and put enough tension on the torsion bars that are part of the equalizer setup to bring the trailer and tow vehicle up to level again. I use my trailer jack to raise the trailer above level, which helps some with getting the torsion bars racked up enough, as doing it with brute force can be quite a job. After the jack is out of the picture, and the torsion bars set properly, the trailer and tow vehicle should look as level as they did when each was holding only its own weight. The reason this is so important is that the equalizer hitch puts some of the tongue weight back on the front wheels, so that the vehicle is not front-end light and steering is not adversely affected. For night driving it also gets your headlights down where they need to be.
Finish the job by connecting your electrical cable, crossing the safety chains under the hitch and securing them, and fastening the breakaway brake cable to the tow vehicle. As you begin to drive, set your inside brake control so that the trailer brakes are doing most of the stopping of the two vehicles, yet are not locking up the wheels causing the tires to leave your valuable rubber on the pavement.