Where to tap power for HEI Dist.

Nothing against Duraspark because it is good, but HEI modules do have some advantages.  If the HEI tested by that magazine was a lo-po OEM style 4-pin, they did perform poorly at anything beyond mid-range RPM.  However, a good performance HEI module does not have this issue.  There are lots of junk HEI modules out there and junk knockoff GM type HEI distributors, but there are also lots of junk duraspark modules.  Like some others on this forum, I run a hybrid of a Ford Duraspark but use a quality performance HEI module instead of the duraspark module.  It works very well.  I generally prefer to keep Ford parts on a Ford, but that doesn't mean the "other guys" stuff is all junk.

Yes, in the start position, the coil gets the full 12 volts, while in run, ti goes through the resistor wire.

I used a relay to power my ignition.  Use the original coil wire as a trigger than run a dedicated 12 volt circuit right from the solenoid (fused).  This way you can use a decent sized wire to power the ignition and you can use a larger gauge wire.