Someone had conical shims. They aren't common. I think I got them from Summit Racing but I haven't messed with the iron heads in 25 years or so.
Did I do a coast down to read the plugs? No.
The plugs should be a dark brown, not black. The tips should be clean.
You need to lean the idle until it pops. The third transition hole is necessary for this to work.
With just two, the mains won't come in until 2,800 to 3,000 rpm. Those will lean out the running mixture.
The reason the idles were originally set up with .70 f mains is that the engine runs so long into the rpm scale before the mains come in.
You only need the heavy idle for that reason and it will pop at idle if too lean.
Since almost all US v8 engines used the 289 Cobra race specs to start with, little development was done with the idles and it was just accepted the engine would idle heavily.
.60 idles are all that you need volume wise and there is now a plethora of idle air holders to mess with. .70's are just from the past now.