Looks like this isn't an uncommon problem:
See here:
http://www.teamswift.net/viewtopic.php?p=81149 , go down to Wed Nov 24, 2004
Looks like you need to work the seals off the valve cover studs to get the cover off.
Or just bring the mini sledge.
(If you do happen to get back there to do this, and it works, can you keep the cam timing belt gear too? I'm not sure if it's identical to the stock one.)