My NOS MSD 6A unit has arrived! Older version but never been touched. Looks like it's just come out of the factory.
Photos to come soon.
These are the instructions I have so far:
Big fat red to battery positive
Big fat black to a nice earth, preferably new one or good clean one on the chassis, not on the engine. (that's another long story)
The existing positive to the coil is removed and connected to the MSD small red
The existing negative to the coil is removed and connected to the MSD small white
The orange from MSD to the coil positive
The black from the MSD on the same loom as the orange to the coil negative.
My MSD blaster coil has not arrived, it is stuck at the airport due to a very long ongoing postal strike
I will use an older Bosch coil I have to test it in the meantime.