This was done in a similar way to this commit, when the change was made from Debian packaging to GitHub's mirror:

https://git.yoctoproject.org/poky/commit/meta/recipes-core/ncurses?id=dfaabf971b02e33870f9f927e9b1356e05e74a17
If I only change the SRC_URI, then it won't find the original 79b9071f2be20a24c7be031655a5638f6032f29f revision.

1003914e200fd622a27237abca155ce6bf2e6030 is the commit hash of the 6.4 release tag:
https://github.com/ThomasDickey/ncurses-snapshots/releases/tag/v6_4

Florin