What spark plug does the factory book call for in a 360 magnum.

Thanks for the reply.
I will hook up another ignition I have and try it.
I only thought the valve spring pressures may be the cause as they are much heavier now and I do not have a timing chain tensioner as it was fine before. Does this seem like excessive play for the dizzy button bearing in mind its just the slotted set up.
[ame="https://www.youtube.com/watch?v=h8_fqMh4Jas&feature=youtu.be"]Dizzy play - YouTube[/ame]