I've hammered in headset cups with a 2x4 and a sledge. It's an all-steel Tange Levin headset, so it put up with that abuse nicely. If it were a better headset or a more delicate frame, I would go to Bicycle repair Collective on Belmont:
http://www.bicyclerepaircol.net/ to have it done.
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Jeff Wills
Comcast nuked my web page. It will return soon..