Re: Transferring a nuc to a top bar.
Well, you could decide to build a horizontal hive, which is shaped like a top bar with vertical sides. Then you could just transfer the frames. More here:
If you want a TBH with sloped sides, cutting comb and frame to fit is one option, or you could do the equivalent of a cutout where the comb is cut off the frame and attached to your top bar.
--- Victor Hugo - "Common sense is in spite of, not the result of, education.”