If anyone else could use it, “s” slightly modified from Miller’s sources (via Udo Munk’s repository) to build on out-of-the-box v7 + C compiler:

https://github.com/athornton/s/tree/v7 <https://github.com/athornton/s/tree/v7>

It’s a reimplementation of Paul Ruizendall’s work.  The changes are:
1) the indirect function call syntax needs to be (*fcn)(arg) rather than fcn(arg).
2) scr_delr and scr_delc needed to be shortened by a character because the linker puts an underscore in front of the name and truncates the symbol to 8 characters, and without that fix they are not distinguishable.
3) isprint() in v7 didn't recognize the space as a printable character

Screen repainting doesn’t seem to be entirely reliable, but…it still works a lot like vi, which I find more pleasant than ed.

Adam