I found most of the clutch head screwdrivers sold by old truck suppliers just junk. Ok to put new screws in clean metal. Handles spin on shank when trying to remove rusted screws.

What has worked best for me is Snap-On has 1/4" drive "sockets". Yeah expensive, sure reduces cursing.
http://buy1.snapon.com/catalog/tools.asp?tool=all&Group_ID=674799&store=snapon-store

Can purchase 3 different sizes at this webpage.

Other way I went was bought some Snap-On clutch head screwdrivers on ebay. Snap-On does not seem to make them new anymore.

Mikey

1951 Chevy 3600 rust bucket with GarWood dump bed conversion
http://www.flickr.com/photos/mikeybs51chevy