It might still be worth hanging on to what sounds like the original fork, at least until you get things worked out. There seems to be some differences in hard to measure fork dimensions that could make a small difference in ride characteristics. This may be less important with carbon forks but I think there is often some length variation there too besides offset, not that any change would be noticeable or bad.
Also, a lot of people prefer quill stems for their easy height adjustment, and that fork might be hard to replace.
I like the mechanics of theadless, especially getting rid of the stem wedge, and can somewhat relate to your situation, but I think a lot of people would be better off sticking with their original threaded fork, even with an adaptor for a new stem. I used to fiddle around a lot with my quill stem height and it was kind of nice to have that easy flexibility.