I copy/pasted an old list from a dcore-stretch install, changed the "-tinycore" lines to "-tinycore64", imported it, and everything worked.
The only oddity was that when I did the import, a few packages prompted me to make choices that I didn't have to do the last time I imported them on the x86 version (which was a couple months ago).
I don't know enough about packaging to know if these prompts were an importing issue, a quirk with packaging, meta-packages, etc., but I thought I'd list them in case it was helpful.
The package "xserver-xorg-legacy_1.19.2-1+deb9u1_amd64.deb" made me choose between "deb9u2" versions for the different architectures.
The package "xserver-common_1.19.2-1+deb9u1_all.deb" made me choose between deb7u7, deb8u2, and deb9u2 versions.
The package "xserver-xorg-core_1.19.2-1+deb9u1_amd64.deb" made me choose from a list of the 3 different debian versions and all of the different architectures for each version (it says there are 65 choices).
I apologize if this is noise, but in the end everything
did import correctly
and worked. Good job and thanks for working on a 64 bit release!