I cannot confirm it works, but it's on order for me. You can get it on Amazon as well.
United Pacific A8004
I think it was $11-12 on Amazon.
It's a generic/universal boot, not just Chevy/GM. But it appears to size up closely.

1961 C60 2T Flatbed (former rural brush fire truck)
283 V8 - 4spd - 21K Miles - 2spd Rear - 2WD - PTO