Ink, paint or dare I say.....scribeI suppose you could use a Sharpie marker with a fine point to get a rough idea. Put a mark on the barrel then transfer it to the housing on both ends, then just guesstimate the middle point. I'm sure that would get you close enough for inital set up. Paint would be more perminent and if your feeling daring you could always use a sharp scribe to make a single mark on the barrel and transfer the end points to the housing........
I made a mark on my .32 main needle with a scribe and its been my soul reference point for almost 2 years now! Works awesome! And I always know exactly where my needle setting is at a glance.
Typically, more than one way to skin a cat......or a carb in this case.
I never had any problems setting up my OS .32's when just setting full travels close to 100% ATV as possible. Never had to do anything crazy to the throttle curve to get my head speeds right.
The only people who truly know where the edge lies, are those who have gone over.