Stephen,
Your options are pretty straightforward:
1. Cut the block off the car, and put another block on with a shackle (I use a spring outside the shackle to keep the block vertical, personal choice).
2. Measure the track and order a new car to fit, put the block/shackle/spring on the new car.
The old Shaefer (I think?) blocks were OK but not great, and even before the sheave splinters like yours did the bearings get pretty worn and uneven. At least that was my experience.
Good luck!
Bill Hawk
Ensign 1414 Prickly Pair
Fleet 30 Austin Yacht Club