Mike,
As you probably know - be careful with what I think is a cast arm (I broke one trying to spread it to fit an aftermarket cable). By the way, I bought cables from 3 different vendors and they were all too wide in diameter.
Luckily, I had a set of GM NOS replacement cables, so I know the aftermarket sets are too large in diameter.
Try drilling/reaming the inside of the "clamps" - step-up in drill size/diameter very gradually - do not drill out more than necessary. This worked for me on one of my trucks.
Be careful - and, good luck.
Tim
