I thought I would start a new thread so you notice this Sean (spelling?)
I am not sure if you're running (hall type) electronic ignition or not, but would assume so as the rest of the car seems to be.
This dizzy cap fits the 18RG (19100 - 88230) old points dizzy, I'n not sure if the electronic one takes the same cap though.
Bosch GD516 (suit 64-69 Corona & S Models)
I hope this helps, I'm afraid that I can't tell you what works or doesn't work for the electronic dizzy, as Owen's electronic dizzy is 18a modified 18RC one.