Jacking under the engine cross member is approved in the service manual, that let's you get 2 jackstands under the frame, just behind the front wheels.
Jacking up under the differential portion of the rear axle is also approved . Then , you can put 2 more jackstands under the axle tubes, or (as I prefer) under the frame just forward of the rear wheels.
if you look carefully, the portions of the frame I indicated are reinforced and will not bend or warp when the weight of the car is on the stands.
Work carefully !! Jackstands are not where I would pinch pennies on cheap imported crap, I prefer heavy duty made-in-USA jackstands if my health & safety are at stake.
The front jackstands seem to be most stable under the control arms. They are more centered with the engine. Mine go under the convex part of the lower control arm just inboard of the bottom of the shock.
I have had the front and rear up individually, I was kinda concerned about the rear when I did it, the stabilizer was/is in the way (under the rear) is there another way to jack the rear up? I tried it ahead of the rear under the pinion area but didn't like it and jacked under the diff housing.
I need to change the brake lines and might as well do the fuel too. The easier way would be to get the trans cross member off, but I need to keep the trans supported. I am not in the mood to drop the tank either.
Also remember that as your floor jack goes up it also arcs back which pulls the car if the jack doesn't roll. As you are raising the car for the second pair of jack stands, watch the first pair carefully to make sure they are not tipping when the jack starts arcing back. If the jack doesn't roll forward when you're going up the car WILL be pulled back, tipping the jack stands.
My personal prefference is to put 2 stands on the frame and 2 on the rear axle tubes, that way you can't set one too low and have it knocked out of the way (the suspension distributes the weight evenly between the two). Also, the further you go from the center of the vehicle the more stable it will be, actual position is determined by what you are working on. On the TTA I usually put 2 under the front swaybar mounts, very solid.