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Where do we start.
The electrics are basic. A wire from the battery to the starter solenoid on the bulkhead and another down to the starter motor. If you disconnect these two cables and touch them together you are bypassing all the ignition circuit and she should turn over. If not.
Things to check. Is the battery set for the correct earth Positive or negative. Originally it would have been Positive earth but could have been converted.
If having jumped the cables on the solenoid and the engine still does not turn over it might be either a seized engine or knackered starter motor.
Try putting the car in gear and rocking it back and forth. If the engine turns that is good.
When you hit the ignition do you hear a click from the starter. If so it could be a bad earth on the battery or on the engine earth strap.
Lots of other things which others will come up with but start with the above and report back and we can go from there.
Lower the hinged center dash panel by removing the two thumb screws and check all the fuses.
Make sure the new battery is fully charged and properly connected. ( Negative cable to chassis / body,
Positive cable to Start Solenoid on the firewall.
I don't think the jumper cables will do the job. Do the above and you should at least have power to lights, accesories, etc. But not necesarily to crank the engine if it is seized.
Check those jumper leads!
Connect them to the external battery and make sure that you get a flash/spark when you touch them together momentarily
If you don't get a flash/spark then the jumper leads or the battery are the problem
If they are OK then connect the negative to a nut on the cylinder head and touch the positive to the starter solenoid terminal on the side which runs down to the starter motor.
That should make the starter rotate.
If that is OK then leave the negative connected to the engine and put the positive on the other side of the starter solenoid.
Then check to see if power is available at the ignition switch or lights. This is to check that the old battery earth is or is not the culprit.