If you have an original Duraspark vehicle with all the hookups and wiring, then its vastly easier to use the matching Duraspark Module.
If its a new installation and a Duraspark distributor is available (or you make one...), then just attach a 78 Camaro 350 HEI module. This is the 4 pin early version which is $18 new.
Higher performance HEI's are available, but if you heat sink this module external to the dizzy it will perform much better than buried inside the dizzy at the engine rear per GM.
1975 Ford Truck 390 FE Distributor (Duraspark) rebuilt, no core, Adv. Auto, $65.
1978 Camaro 350 Ignition Module (HEI), $18.
Heat Sink, $2.
Wire w/1/4 female spade connectors (7) and coil/ground connectors, $5.
TOTAL: $90
NOTE:
1. HEI module has FIVE (5) connections, mount screw is ground -> dizzy.
2. Power must be 12V, careful retrofitting ballast resistor setups.
3. Need heat sink and special grease (inc w/new HEI). (2x2x1/8x4 AL angle)
4. Tie all leads so vibration cannot separate spades.
5. Most Duraspark's came in trucks or large cars, recurve helps (see web).
6. Get rid of the large dizzy cap, use the 60's small cap & wires, its vintage correct.
(usually just remove the later adapter collar and voila it fits)
7. Converting an earlier Ford dizzy to Duraspark is easy, use a $10 5.0 donor.
8. Most popular 12V coils work.
9. Prefer not to cut dizzy leads as this complicates a field replacement.
Search the web for "duraspark HEI conversion".
Wiring Diagram for 5th graders here:
Dirt cheap Ignition