ok, please forgive my lazy ass for not posting revised instructions for ages.
This isn't exactly how they do it, I've changed how the tapers are done to give a better result but this is how i get 'er done now days

This is for atrax ropes and similar constructions only, other 24 strand lines may have different core constructions, i.e tachyon.
Tie knot approx. 3m from end of rope
Jacket taper and marking:
Measure 750mm from rope end and mark jacket (mark A)
Measure desired eye length and extract core (3” works well)
From mark A mark 300mm towards end (mark B)
From mark A mark 500mm towards end (mark C)
At mark B, taper jacket by 12 strands towards mark A, remove one chevron pair, skip one pair, remove one pair etc until 12 strands removed. (you can cut these shorter but do not cut them flush, leave approx. 100mm)
(For black widow, it is 8 strands tapered in the same pattern)
Core taper and marking:
Milk line from knot repeatedly until core does not suck back into jacket anymore
Mark where core exits jacket
Mark 5 and ¼” from exit mark away from end of rope (mark CA)
From mark CA mark 300mm away from end (mark CB)
From mark CA mark 500mm away from end (mark CC)
From mark CA mark 700mm away from end (mark CD)
At mark CD taper core away from end, remove one doubled chevron pair, skip one pair, remove one pair etc until 6 doubled strands removed (12 total individual strands). (you can cut these shorter but do not cut them flush, leave approx. 100mm)
Crossover:
Burry the tapered jacket from mark CC past mark CD in core exiting where you finished tapering the core
Burry the tapered core from mark C past mark B in jacket exiting where you finished tapering the jacket
Milk this assembly tight making sure crossover point is smooth
You should have a small amount of core and jacket exiting where you finished the burry, mark where they exit, pull them out slightly, cut at the mark and taper ONLY 30-40mm of the end, taper these conservatively, if tapered too much this will result in necking at these points ruining the splice.
Suck the tapered ends back in, tension the eye and burry the splice cutting the taper strands flush as you go. You will need to use a prusik to milk from the knot to the eye to completely burry this splice.
Finally secret whip from the eye down a minimum of 100mm