Interesting problem. As was mentioned, how are you diagnosing a bad coil?

Is your car supposed to have a ballast resistor or a resistance wire in the primary ignition circuit?

Do you have the correct distributor?

I would insert an ammeter ( on a high scale first, then lower it )in the feed to the coil to see if any current passes through the coil when the ignition is not on. A constant current, no matter its magnitude might warm the coil so that it gets too hot during engine operation, shortening the life of the coil.

Could the output of the coil have a relatively high resistance short to ground, causing higher current than normal.

Then I would observe how the current varies when the engine is turned over. This should, vary with no current when the points are open.

Then I would try the same experiment with the regular feed to the coil disconnected, and a wire directly from the battery. through the meter. Compare the results.

If this does not produce a difference, I would try both experiments when I cranked the engine over with a wrench.

Let us know what you have tried.

I would also open the engine wiring harnesses to see if anything funky is going on inside them. Didn't some 80s Volvos have engine wiring that deteriorated ?

I was told that my '88 GLE had a 240 motor in it - perhaps your car has a similar oddball construction.