I didn't look at any pictures. I thought it was common knowledge that blowers require double keyways on the crank.

Whether or not he has to have two keys is a simple computation if he knows the torque output from the blower. We would also need to know what material the crank and pulley is. The key can be made out any variety of materials that satisfy minimum strength requirements.

If the crank keyway is too trashed other options may have to be considered as well.

It is certainly not a unique problem however!

Kitz