what about this?

%dw 2.0
output application/json
var contentVersionVar = "068DQ000000lK0iYAE"
---
{
    documentItemToSigner: (payload map (item, index) -> {
        typeCd: item."typeCd$(index+1)",
        subtypeCd: item."subtypeCd$(index+1)",
        eSignLiveExtension: {
            extractInd: true // where does this come from?
        },
        documentItemName: item."documentItemName$(index+1)",
        TEMP: item.contentVersion
    }) filter ($.TEMP == contentVersionVar) map ($ - "TEMP")
}