[Coupeguy2001]

First, I would get a fresh piece of cardboard, and put it under the truck over night.
If the cardboard has a couple drips, you can schedule a reseal at your leisure. if it has teaspoons full , it is a top priority thing.
Look on the bright side, that much oil will discourage rust!

You did not tell us if your truck has a one piece rear seal or two piece.
A one piece seal can be pried out and tapped back in place with a new seal. You can get it out by removing the trans, and bellhousing if a stick shift, .... Flywheel and torque converter if auto.

Then decide if the engine needs a rebuild. Like previously mentioned, compression check will tell the tale.
Next, have someone other than you start the engine cold. Does it smoke?
Then shut it off, and start it in 5 minutes. Does it smoke now?
If your anser is no to both, you don't need a rebuild.

If your answer is it smoked after sitting all night, it might just be valve seals.
In your truck, a fair amount to pay for that might be $200, depending on how fast they get it done.

Does the engine use a lot of oil if you drive it for a couple days, and not much on the floor?
If so, it might be pumping oil past the rings. Compression check will tell you more here.

If you take a compression check, and you have low compression, say 115 or lower, take a small syringe, and inject some oil into the cylinder through the plug hole. If the compression goes up about 20 pounds, you have bad rings. If it doesn't, you have probably bad valves.

Now with an air hose screwed into the plug hole, listen for air leaking out the tail pipe, or coming out the carb. If it's the tail pipe exhaust valve is bad. If from carb, it's the intake valve.

If the leak is not severe, and this is the first you notice it because somebody said something, then keep on driving it, because apparently the leak didn't bother you.

I would change rocker cver gaskets and maybe timing cover and pan gasket, but replace the pan gasket with a one piece pan gasket for your engine. They make them in both varieties, single rear seal and two piece seal engine gaskets.

The Chevy engine is a tinker toy. You got the right engine to learn if you are so inclined.