Single vs. Dual Vacuum Distributor

Greetings

I have an old '67 Ford with points ignition. I have learned that I can get a Duraspark setup from a 75-76 pickup with a 360 (also an FE block). The local discount parts store sells reman. ones for $63 plus core. Cool, but there are two choices - single or dual vacuum. Which one is better? The dual vacum also has a $15 core charge vs. $30 for the single. I won't have one for exchange.

I have done this upgrade on another car with a 289 and works well.

Thanks

If anyone cares, I finally got rid of the old points setup. I did the duraspark upgrade with the single vacuum distributor because the dual vacuum one wasn't in stock anywhere. I wish I would have done this a long time ago. Now I can run regular unleaded, timing isn't retarded, and no knocking or pinging. The distributor and control module were about $115 including the $30 core.