Well, sitting here now just a bit chagrined... using an awl, I was able to poke through the bubble of coating and exposed the hole. Indeed, a plug (rubbery/cork like substance) must have been inside the thread (funny 'cause this is not an issue on any of the other threaded bosses on the frame). I then used a clean exacto blade and cut some of the material away. Looks like I'll need to pick at it, using tweezers and I'll see how that goes. If I have trouble picking out material to get the threads clean, I'll try dabbing some Goof Off (using a Q-tip) inside the hole to remove any persistent junk... it appears the tap will not be necessary (sigh), and will forgo the aircraft stripper.
The Cutting Oil sounds like an interesting idea... I haven't attempted to thread any other bolts yet, so I'll swing by the hardware store this morning and see if I can p/u a small can.
Re. the Bushnell Eccentric, it appears that by using the Bushnell I would not need to worry about the existing threaded lock bolts, do I understand this correctly?
Thanks for all the input, looks like my weekend assembly will proceed as originally planned (whew)!