Direct Coil Control
If you have a 3500 that has a 24x LS1 style crank reluctor, then you can build your megasquirt to run the factory direct drive ignition. There are a couple of advantages to running this ignition type over GM DIS. First, the ignition control module is removed. This is a common failure point due to it susceptibility to vibration and heat. The LX9 ignition also features iridium tip terminals and plug wires. Factory wire size is 8mm.


If you do not have this ignition available, you can modify your GM DIS ignition control module for direct drive. Directions are here.

If you choose direct coil control, you can have the megasquirt drive any coils you'd like, as long as they have internal ignigtors. An example would be LS1 style coil near plug or any other coil on plug you could think of. Since there are only 3 spark outputs, the coils will need to be run wasted spark (1&4, 2&5, 3&6).

EDIT: Theoretically, you can run direct control coils with a 7x sensor and a cam sensor. Follow these directions but select 7x instead of LS1 for spark mode.