IMO one of the fundamental issues with the two piece cam in this application is the pressed on piece is in front of all the twisting load.

Potentially you could be trying to rotate the cam against 16 springs that have 400lbs closed/1200lbs open load(times the rocker ratio)...... along with some bending forces perpendicular to the centerline, and throw some oscillating/harmonics in the mix as well.

What’s going to insure the indexing between to two pieces doesn’t drift?

Good point, the odds of success in a two piece design are much better when the cam drive and the distributor drive gear are at opposite ends rather than both in front.