What do you guys think is the best plug to run when running these heads?

 

I don't have them, but from what I've read, it depends which model Edelbrock heads. You have to be careful they don't stick down too far. This was a response to a question on the Flathead Forum; it is copied from Edelbrock's site:

• SPARK PLUGS: A 14mm, 3/4” reach, gasket seat, 5/8” hex sparkplug is recommended, such as Champion RC12YC, RC14YC, or equivalent.
Heat range will vary with different combinations and conditions. Use anti-seize on spark plug threads to prevent thread galling!

I wouldn't use Champion personally, Autolite are more reliable IMO.