Hi Mike
Not sure about the electronic ignition part of the question, but otherwise it's a straight swap (provided the curves are the same). My GTL originally had a Femsa unit which was okay when it worked, but I found checking the points gap and changing the points much more of a hassle than with Ducelliers, so I eventually fitted a Ducellier unit.
I've found Ducelliers much more user-friendly - it only takes a moment to check the points gap. The only problem I've had is with the hole in the baseplate that the screw that holds the fixed part of the points goes into - over the years and with multiple points changes/adjustments the hole can become bigger. If you're lucky, you might find a Ducellier with externally adjustable points; they're really good, as you can adjust the points without removing the distributor cap.
The other advantage of Ducelliers is that points/caps/rotor arms and condensers seem to be much more widely available than their Femsa equivalents.