On the spark plugs: If you have the "Peanut plug" head, the plugs that I suggested are a Platinum type to get the extended electrode. The standard NGK is not extended.
When you install them, you can run the gap wider than spec due to the small electrode, as long as your ignition is in good shape. The reason for this is that it takes less voltage for the spark kernel to propogate with the smaller electrode. Where a weak ignition is in use, platinum plugs will improve driveablility at the OEM recommended gap. This is generally not as much of an issue with newer ignition systems, but can play a roll with older electronic types.
There is no reported benifit to running the gap wider than .045" in our case with the slant six. Retime the engine to make sure your base is at the recommended starting point whenever you experiment with changes in gap. Introducing changes in timing can create apparent changes in mixture calbration. These changes are normally quite small, but it's a good thing to keep in mind.
If you choose to index the plugs, there are two trains of thought on this. One is to allign the ground strap so that the open part of the plug is away from the quench area, facing the center of the combustion chamber.
The other is to have the open part of the gap facing the exhaust valve. This causes the flame front to burn the charge in the vicinity of the exhaust valve first. As the exhaust valve is the hottest area in the combustion chamber, this will minimize detonation in the chamber.
The chamber of a slant six is pretty open, and the plug is inserted into the chamber at an angle to the bowl, so the first consideration doesn't really apply. Most of the racers only index plugs to improve piston clearance in highly modified engines. I've not heard any report of performance improvements from indexing.
Where lean calibration is used, minimizing detonation is a consideration though.
In other combustion chamber configurations, some benefit to indexing away from quench zones and toward the exhaust valve could be useful. One of the first orders of business when doing head work is to round any sharp edges. Those sharp edges can become hot spots in the engine, leading to detonation. Accumulation of carbon in the combustion chamber can lead to hot spots and detonation as well.
Another 2¢
CJ