primary resistor uses to be between .5 and 1.5 ohms

secondary 5 ohms.

several ppl has got success modifying the ballast ( per an idea I posted once ) to the ballast bypass replacing the resistor with a jumper wire on ceramic groove to those ign system doesn't need the resistor anymore ( such as FBO and some others ). In that way you don't need to hack the wiring and still keep the stock look on firewall, and get it back to stock just replacing the ballast again remaining the wiring untouched. The white stuff is simply epoxy, easy to remove.

now, using a dual ballast in place of the single ballast just to hide the diode, Dunno if will look right a bigger ceramic piece and unused prongs there. Simply wouldn't look right. If you already got a single ballast, is better just install parallel the diode between ballast prongs ( solding or using dual male/ single female spade kind splicers ) and protecting with shrinking tube. I think would be less noticeable than the weird uncomplete bigger ceramic stuff. My idea came on if already using a dual ballast with double plugs on engine harness