Originally Posted by sp2816
On my 539, I run the Dart 320 heads along with Ross pistons. I had to cut "fire slots" in my pistons, run the Autolite race plugs, and index to keep from closing up the gaps. I have two different sets of the Dart heads and one set uses the gasket seat plug AR3933, and I have also used the NGK plug R5671A-8 (stock #4554). But the other set of heads use the tapered seat plugs and I can't remember the numbers, right now.
Bill M
When you do the freshing up on the engine, you might want to look at using JE pistion. They already have the fire slots machined in them. We had the same problem with the 565 ci and the 598 we use now.