Lo again,

redoing the complete procedure i noticed, that i must have mixed up some revisions..
it is not necessary to do any changes to jars.xml. sorry about this mistake.

this procedure should be working:

1. checkout http://svn.apache.org/repos/asf/cocoon/trunk in rev 351990

2. checkout http://svn.apache.org/repos/asf/cocoon/blocks (i used rev 351990 - rev. number changed automaticaly)
(into folder cocoon/src/blocks)

3. checkout http://svn.apache.org/repos/asf/gump/metadata/project/cocoon/module.xml in rev 351990
(into folder cocoon/src/gump/)

4. copy local.build.properties and local.blocks.properties from
apache-forrest-0.8/etc/cocoon_upgrade into cocoon/

5. build cocoon

best regards
llamar