1983 could have 2.0l or 2.3l gas engine, or 2.2l diesel engine, but carb rebuild makes the later unlikely, lol.
Block test is a bit misleading in name.
If there is a leak between an engine cylinder and the cooling system the exhaust gases from that cylinder will be forced into the cooling system.
A block test uses a chemical in a tube that will change color if exhaust gases are present.
The tube is placed over the rad cap opening and air is drawn from the rad thru the tube/chemicals, using a hand pump or engine vacuum if running.
If exhaust gases are present the chemical will change colors, it happens very quickly and leaves no doubt.
It doesn't test the block or head, lol, it just tests for exhaust gases in cooling system which indicate a failure in the system.
You can do a glove test to check for head gasket leak as well
Fill system with water/coolant, leave about an inch of air at the top.
Place latex glove over rad cap opening, use rubber band at base
Remove overflow hose and block off rad opening, vacuum cap or finger is fine
Cooling system is now sealed or should be.
remove coil wire, you want a no start
crank engine and watch the glove
if glove bounces you have a head gasket leak, or cracked head
The 150psi compression from leaking cylinder is being pushed into cooling system making glove bounce.
If you remove one spark plug at a time and crank engine, when glove stops bouncing then last spark plug removed was from the leaking cylinder, put it back in to confirm.
This can help you later on when inspecting for gasket failure or cracked head.
1983 4cylinder gas is a Lima engine, Lima 2.0l/2.3l/2.5l all used the same block and share many of the same parts, 2.0l block was bored out for 2.3l, and stroke was lengthened for 2.5l.
Parts are easy to come by, new and used.
Good project truck, no computer or other pesky electronics to learn about, has a timing belt which should be changed if you are removing the head, so you will learn about valve piston timing