To answer my one question, one can do the following:
eachFile { fcd ->
String sourceName = fcd.sourceName.replaceAll( /\.txt$/, '')
String content = fcd.file.text
fcd.filter {null}
fcd.filter ConcatFilter, append : project.file('src/templates/my.template')
fcd.filter ReplaceTokens, tokens : [
token1 : content,
token2 : sourceName
]
}
It is very importtant that no filters must have been added before String content = fcd.file.text is executed. This is due to Combining eachFile & filter results in failure. The only way of adding filters are within the eachFile and only after extracting the content of the data file.