It has been a few days now, Are you running?

You haven't mentioned if your headlights work (with ignition on and light switch in headlights)?

The lights will draw a lot of current and should tell you something about your electrical paths.

Did you try to jump start the car with the jumpers - to - and + to + at the batt, unless your batt is 60 years old it has flame arrestors.

You say that running a jumper from the block to the body allows something to happen. this makes it sound like you have a floating ground somewhere.
It would also make it seem like the body or the block is electrically charged, IT WILL BE!

If you have floating ground the car also will not charge the batt.

Check Batt voltage. is it at least 11 volts?

Do these tests:

Turn your ignition on.
Turn headlights on.
Take a volt meter on DC:

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Note:
If you don't have a volt meater use a 12 volt test lamp, in the following test the lamp should not light.
If it lights brightly it means a fully open ground.
If it is dimly lit it means a ground with resistance.
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Check the voltage between the body and the block.
Check the voltage between the neg batt terminal and the ground.
Check the voltage between the neg batt and the block.

All of these 3 readings should be 0 volts.
If any of the above gives you a reading close to your batt voltage it says that that path is open.

If you get a reading somewhere between 0 and your batt voltage it says that your ground in that path is not perfect and has some resistance.

note rust is an insulator.

Checking these 3 voltages will tell you a lot about your grounds.

If all your readings are zero I would hook the cables up to the other car get yours running and then do these three tests again.

If your grounds are good you will get reading of 0 again.

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Note:
Introducing the other car and the running engine will get plenty of current flowing through the grounds.