Knowing that I might open a can of worms, here I go:
I have been monitoring this group for almost a year now, and have not seen any information posted on the original BITX20 during that time. I also did a search on the files section and could not find information there, except on how to modify a BITX20 3 series to be multi band. Granted that I used BITX20 for the filter, and there may be a better choice. Even the history document is not clear on what the early designs were for the BITX series. I would assume that the design that you built is VFO controlled, rather than Si5351 based similar to the original BITX40 that later was modified to include the Raduino with Si5351.
There hopefully are others on the feed that did work with the original BITX20 that might make sense of your questions. For me, I would need the schematics at least. I would suggest that you point us to the information that you have on that original design so that we could make suggestions.
Alternatively, wait and hope someone that worked on the version that you built can chime in.
73 and hope someone can help you.