Yes it is..... What do you read on the ohmmeter when you connect the alligator clips together? Do that and subtract the amount of the lead resistance from the actual reading. With these low resistance values, you need to correct the resistance readings to remove the lead resistance.
The value of the resistance reading on the lower half of the ballast looks too high, even with lead resistance subtracted out. This is the main power feed to the coil and it should be < 1 ohm, cold. Factory cold resistance is actual close to 0.6 ohms, cold, and around 2 ohms hot. When the ballast heats up, that resistance goes up, and a 3 ohm cold ballast resistance will probably be 6-8 ohms hot. That high resistance will kill your spark energy, and may explain why the car craps out when it warms up; the ballast takes 30 seconds to 2 minutes to get warmed up and increase its resistance.
Not all replacement ballast resistors are right so I always try for an OEM one. I can understand why this may be hard to get in Poland. Can you get the single MSD 0.8 ohm ballast resistors over there? That is a good backup part for the lower half of that ballast.
And the spark plug wire resistances I gave you are general numbers that I use for troubleshooting. But when the resistance wires get old, their resistance goes up and it eats up spark energy.
Did you check the resistance into the distributor pickup yet for less than 500 ohms?
The plugs look like carb as you say. But the general description of 'craps out after for a while' points to the ignition failing when warm/hot. This thing has been serviced with who-knows-what-parts, so a thorough ignition system check is needed. Don't tune the carb until the ignition is right.
