update on a couple things for the folks who might have been interested in what's next:
1. ordered Tange Passage HS from an ebay seller at $15 shipped. totally economic even if it goes failure.
2. contacted Frank The Welder in VT. nice guy, replied right away with logical info. i had asked him to estimate both Threaded & Threadless extension. he suggests only
Threadless conversion due to that
A. he'd need internal reinforcement B. but to avoid where the quill stem engages, that reinforcement point would be forced to too close to the crown. basically because the tube is too short. cost was fairly high—understandably so but way beyond the budget for this project unfortunately. good to have learnt, tho, that such a thing can be done & how & where.
will update when i have a result of
#1 . crossing fingers!