which .223 bullets in the approximately 75-77 gr range can be seated to mag length? conversely, which cannot?

Hornady 75 BTHP (and TAP T1), Sierra Match King 77 and Nosler 77 BTHP are probably the most common bullets in that weight range and can easily be loaded mag length.  Privi Partisan makes a 75 BTHP bullet that can be loaded mag length and is a little cheaper than the Hornady, SMK or Nosler bullets, though you shouldn't expect the same accuracy.
I have had great luck with the Hornday 75 T1 bullet for both accuracy at the range and terminal performance while deer hunting.

Hornady 75 A-Max on the other hand can not be loaded mag length without seating below the ogive.

The Berger 75 gr LTB was designed to be loaded to magazine length, too.