OK, some sort of success. Downgraded (TWICE!) to JaS 10.4.8 SSE2/SSE3. First time I ran NB, it crashed with an error message about SDL_Quartz_Window leaking like a macrame diaphragm...
After switching from Titan.kext to Natit.kext to Natit_Dual.kext, I can now run Neverball (about 150fps on easy 1). Unfortunately, I think the reflections aren't working - on starting screen, halo is reflected under platform, and on subsequent launches, it runs very choppy, with the FPS going from approx. 20 to approx. 150fps. I have reinstalled AGPGART1.2, and now I will experiment with different AGP Aperture sizes (was set at 64MB, need to check at 128, 256, 16, 32MB). Not only is it not crashing, there are no extraneous error messages when launched from the terminal.
PS. Neverputt is working like a charm - 250 to 500fps - smooth as silk!
PPS. Is it possible to build an Intel-only build? I would appreciate that very much...
Celeste and Electronic Super Joy