Billy,
I have my '68 up off all 4 wheels right now... Put it up yesterday. This is what I do--and tomorrow, I will take pictures for you with my jacks in place and where I place my stands and post them:
First, I never jack my car(s) up with one jack! I have two floor jacks that I use simultaneously. If you are going to work on your car, go buy another jack to use; I like the the low-rise models.
You also need to buy two sets of jack stands! A car should never be left up on jacks--especially with the wheels off!!!
I wheel the jack in the center of the back of the car and put my jack right in the center/bottom of the differential case/pumpkin/rear-end oval/round thing that hangs down low on the rear axle. There is a nice, flat place that perfectly fits the round plate on the floor jack. I look from the rear, then go and look to the rear from in front of a tire to make sure it's centered before I lift the car. I often (usually) work on gravel, so the jack won't roll and placement is very important--but you should look from at least two directions/angles, anyway, before you lift the car. You will be partially climbing under the car on the jack and you need to be as safe as possible. I then lift the car from the center section and check the jack placement a few times as I go up. Once the wheels are as high off the ground as I like, I take my two jack stands, place a rag on the top, and center them on the axle to either side of the pumpkin--not in the center between the wheels and the pumpkin, but more out--toward the wheels. Make sure there isn't a stray brake line there. Rise up the jack stand top portions to almost touch the axle housing and put your rag on top. Slowly lower your floor jack and make sure the stands are centered with the tops on the axle housing and that all four feet of each stand is flat on the ground.
Next, take a jack to either side of the car and aim them under the front portion of the door. Look underneath--you see the floorpan, and the frame rail segment (the long, tubular square chunk of metal that hangs down lower than your floorpan and runs parallel to the edge of the car). You will see the back end of that frame rail segment--follow it forward. It will meet an almost flat piece of metal that attaches the outside edge of the car to that rail; this piece of metal is roughly 18" wide and 12" to 18" long. This flat metal piece is joined to the floorpan with a small wedge of metal and on the driver's side, there is a metal line that goes inside (the gas line). This is the torque box. I place my floor jack on the torque box, where it meets the frame rail--there is a reasonably good place there that is flat. I situate the opposite jack on the opposite torque box (1968 and up) and I lift each side a few pumps of the jack and go back and forth, lifting the car fairly evenly. This tends to keep the feet of the jack stands you've placed on the rear axle housing flat on the ground.
I place my front #2 jack stands forward on the front frame rails. Look underneath the front bumper--you will see the radiator support, which is a solid piece of metal running from on side of the car to the other that the radiator is bolted to or affixed in with clamps. From the center of the car, on each side, looking at the radiotor support, you will see flat/tubular pieces of metal that run up the this support and are welded on. NOT the flared metal pieces that are hollow on the bottom--what you want to use look similar to the frame rail beneath the floor pan you where jacking to. I place each jack stand as far forward as possible, behind the radiator support, but on these front frame rails. I place rags on them as well and very slowly lower each side down, onto the jack stands--watch that these sit flat and are supporting the frame rails evenly.
Many of my cars have sat for months to years like this, while I work on brakes, wheels, whatever. And it gives you a wide-based stance such that the car is very solid and not tippy. If you are going to do work on your cars, you need to have the proper tools (jack stands and floor jack) for your safety, and for the safety of your car!