Since it was my idea that you ask around for the answer I thought I'd post here too. Now that I read the description closer, they claim it can be used in either orientation. The one application they list it for is for a weldless thermometer. The fitting for my sight glass is literally the same in that it presents a male 1/2" pipe thread to the bulkhead.
As I suspected, it will go sight fitting, coupling, nipple, kettle wall, Oring, Washer, stainless lock nut. They made a point to use a stainless locknut knowing that it might be used on the interior of a vessel.
If the weldless bulkhead works at all, as it should, it will certainly work for my sightglass. Just make sure that the place you drill is as low as possible but still leaves room for the Oring to seal well.