Michael,
Congrats, a huge accomplishment on a huge engine!. I'm sure Waukesha has specs for this beast, but here are my thoughts. Old stovebolts usually idled at around 500 RPM. It probably depends on how the engine is engineered. Your big Waukesha might be different...it's sort of a tune by ear deal, whatever sounds good!
The timing issue is about the same. Although the engine was designed to work best at a specific degree of advance, this is not etched in stone. Most agree that more advance is better, it tends to make more power. More advance will usually make a engine run hotter, and under a heavy load, ping...these two items can be used to tune the engine.
You don't want to effect idle speed by turning the distributor, you will end up losing advance. Highest idle RPM using distributor timing isn't correct.
You tune your carburetor's idle circuit to achieve maximum RPM, then set the RPM as desired with the idle stop screw (?).
As I read what I wrote, I am not sure I actually answered your original timing question. On a "conventional" gas engine, acceptable timing can be achieved by advancing until increased engine temp is observed, and/or the engine starts to pre-ignite..ping, under a moderate load. These methods are in lieu of using factory timing specs.
On your engine, I would try to find the factory specs and tune to them. I don't know if there are true "timing marks" that can be viewed when the engine is running, but those would be the ones to use.
Some of the industrial type engines had holes that lined up and a pin was inserted into them, and the system was tuned from there. If you have "viewable" timing marks, and can attach a light to #1 cylinder, I think this would be the best way. Hope some of this makes sense and good luck.
Stuart
