I've replaced the head on my 66 Series IIA 24V FFR with one from our host. Since the new head had an 8 stamped on it, and it's thinner than 3.590, I'm assuming it started out as an 8:1 head and got milled down.
I did change the pushrods to accomodate the change in geometry.
My question is do I need to run different plugs other than the FFR ones that are currently with the vehicle?