The coils don't ground through the spark plugs: OK, the high voltage secondary does "ground" through two plugs but that secondary HV part of the coil should have no direct connection to the bike's 12V power.
So no way the plugs can blow a fuse.
Your coil may have failed and be drawing way too much current. That happens. Rarely.
The coil gets +12V power through the MAIN fuse and key switch, through the kill switch. The ground connection to each coil comes from the points., when a points set opens and removes the ground connection, power is cut to the coil, and it generates the spark voltage.
So a main fuse blowing could be a bad coil, more likely it's a wiring harness problem - a wire worn through or melted and touching where it shouldn't - or a problem in the kill switch or key switch.
You should have a meter that can measure the coil resistance. It should be close to 5 ohms, but meters do not usually measure accurately at low resistance. As longs a the two coils measure pretty close together they are probably OK. If one measures much lower than the other then it's probably NFG.
Since the problem seems related to the one coil check the wiring to it carefully.
