John,

If you burn another one up, suspect your ECU.  The "transistorized
ignition control unit" in the ECU controls both the voltage and firing
of the coil. These  coils don't appear to have an internal ballast
resistor, so if the ECU is not doing its job the coil will get a full 12
volts which will overheat it.  I am making this assumption since the
primary coil resistance is a very low .5 ohm, according to the Bentley.

To save the cost of replacing the ECU you might try adding a ballast
resistor in series with the + side of the coil.  Might work.

Good luck,  problems like this are extremely annoying!
--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia
'65 MGB (Driven since 1969)
'74 MGB GT (Restoring)

Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Parts cars:
'68 & '73 MGB, '67 MGB GT