OK, back to basics!
You need fuel, air, spark, and compression, all at the right time.
Start with fuel- - - -does the fuel pump squirt a good stream when the engine is cranked over with the starter? Disconnect the fuel line at the carb, and plumb it into a catch container like a coffee can. It should squirt a good, solid stream of gasoline as the engine is cranked. If not, trace things back until you find the restriction. A reasonable amount of air pressure applied to the line from the pump to the tank should cause bubbles in the gas. Just blowing into the line should be sufficient to bubble air into the tank.
Next- - - -spark. If you've got a standard point-type distributor, the coil wire should jump a 1/2" spark or longer to ground as the engine is cranked. If it's weak or nonexistent, check out the points, condenser, and internal wiring in the distributor. The older ones were bad about getting breaks in the primary wire from the coil to the points. With the points open, there should be 12 volts all the way to the insulated side of the points. Points closed, ignition switch on, 9 volts at the coil (+) side, 0 volts at the coil (-) and to the points. If there's 12 volts at the insulated point with the gap closed, the point contacts are burned, and not conducting. On a HEI distributor, it's difficult to check anything but resistance of the coil, so substitution of known good parts like the module and pickup coil is the only option available to the non-professional without a shop full of fancy equipment. Look out for a distributor rotor with a hole burned through the middle to the dist. shaft.
Compression- - - -about 100 pounds on all cylinders is enough. If ALL cylinders have low compression, you're probably dealing with a slipped timing chain. Here's a quick cam timing check. Take the passenger's side valve cover off, and roll the engine over by hand with a socket on the crankshaft pulley bolt. It's easier to do this if the spark plugs are removed. Watch the third pair of valves from the front (#6 cylinder). The exhaust valve will be about halfway closed as the intake starts to open, and the Top Dead Center mark on the crankshaft pulley should line up with the timing mark just as that happens. That's called valve "rocking", and if the timing mark is much past top dead center when that happens, you've got a badly worn, or slipped timing chain. Another check is to rock the crankshaft back and forth, and see how far the pulley moves before the distributor follows. More than 10 degrees of movement at the crankshaft before the dizzy moves means the timing chain is stretched and/or the sprockets are worn out.
Jerry
