[LH Lead-Foot]

In the beginning of this "Electrical Forum" are good wiring diagrams. It is in color but uses legal paper to print. Either way, V8 or In-line 6, the diagram is about the same.
These where paper service manuals with electrical schematics in the back of the book that folded out onto 2 pages. Headlights on the left and tail lights on the right.

The OEM fuse box under the dash is held in place with two (2) 5/16" screws (Maybe 1/4"). You have to remove the 4-way flasher to get to the top RH screw. Get a good light under there to look. Let screw is low / right screw is high. Goes into the firewall to hold in place. Bulk-head connector pulls apart after that with one top half & one bottom.
The starter wire circuit begins at the ignition switch. B+ to the switch is battery voltage. The back of this switch is marked with "S" as start. That connector has a 12 AWG wire that is PPL. It passes behind the fuse box, goes thru the bulkhead / firewall connector. This where the problem may be.

I have a Fluke 87 Type-V with a life-time warranty...It's about $500, plus Vetronix Master-Tech with lab scope / ignition module.

Once again, do you have a digital Volt-Ohm Meter (DMM)? If not, they are cheaper than ever before and the more you spend, the better that are. But even lost cost ones will work.

Electrical Testing:
A test light to ground, will tell you is you have voltage. Just not how much. Is the light bright or ok? Who knows...but a good place to start. A DMM will allow you to see if battery voltage is at the ignition switch. Test battery, then ignition switch B+ RED wire to a good ground, like un-painted E-Brake bracket for ground.

The PPL wire in the crank position should read the same as the B+ at the switch. If not, you have a bad 50 year old ignition switch. If it is the same reading while cranking, then re-position your meter led to PPL at ignition switch and PPL at the starter. (Note: If Radio Shack is still around / they sell "Meter led Wire" on a roll. It is soft covered wire and you can solder clips on both ends / I have 5 different lengths in my tool box) Try cranking, use a buddy to crank & disconnect the distributor so it won't start for safety.

If it does not turn over, the voltage reading from switch to starter solenoid will read less than 12 volts. This indicate a loss of voltage or "Voltage Drop". Now you remove the inside fuse box, check the PPL wire in the top half middle of the bulk-head connector. It just pulls apart. Look at both sides.

Testing with Fuse box in place:
If the voltage reading is less than 1 volt from switch to starter, the starter solenoid/starter is the problem. This is a series circuit & the solenoid & starter will use all of the voltage in the circuit. But at this point, is not working.
Inside the starter or a mechanical problem with then engine. Socket and breaker bar on front pulley to rotate clockwise to see if it turns...not locked.

Check the battery for clean ground connections. Look for the ground wire tight & clean on the engine, usually at the water pump or alternator bracket. Look for a ground wire from the battery to the fender for chassis ground. You should have one next to the battery. Proper up-dating, is to add one from the engine to the frame also. Don't forget the battery connections as well. (But you told us it will crank with screw-driver)

Hope this gets you going. Ignition switch, bad PPL connection behind fuse box, Bad starter solenoid (But you said it would jump with screw-driver / so good), but check engine mechanical for crankshaft movement.

Otherwise, you have a bad switch, PPL fuse box connector, or bad wire. The male to female terminal connections fit should be tight. They can be removed, pinched with pliers on edges, then fit tighter. This is loose terminal, loss of voltage with current going thru it (For test voltage drop) resulting in loss of current to operate the starter's solenoid.

Best of luck. Sorry to be long, but have done this for years & taught it for years.