Are you going to use an MSD box or Ford unit with the Duraspark distributor?
I don't think you will need a resistor with the Duraspark. I have a MSD 6A with a Duraspark in my '66 Fairlane, no resistor.
I'm building a '68 Fastback for a guy. It has a 428 with Duraspark and MSD 6AL. He had the motor build by a Ford FE specialist. No resistor.
I've looked at several wiring diagrams on both car and have not seen a resistor in the circuits.
Maybe someone who really know will post.
This post caught my attention because I took three Duraspark distributors apart today.
I'm trying to recurve the one on my Fairlane. And adjust the vacuum advance.
I had a question about the bushing on the pin to limit the total advance. I removed parts on the 68 Fastback distributor so I could see the pin. I bend one of the springs so I will have to replace it. Called a buddy and he said he has one. Lucky me.
I've learned a lot about Duraspark today. I do like them.
good article on tuning Duraspark
The Ultimate Duraspark Distributor Timing Guide.