stock location appears to be about 6 inches in front of the battery and about 6 inches down from the edge of the fender. Like I said before there are 3 dimples in the fender. Look closely.

 

Thank you again, Twitbeck.
Yes you said before but I didn´t expected the location that far from heater pipes.
Didn´t see the dimples in the fender because I mounted my MSD box exactly on this position .... your pic helps !