You'd be better off taking your old report and splitting it into 2 big pieces:
data preparation where you'll retrieve, sort, aggregate and HOLD your results, and
data presentation where you'll take data from the resulting HOLD and display it in any format you need (that's how I do it anyway).
You could then put the data preparation piece in a .fex on its own and "invoke" it from the old report via -INCLUDE.
Once that works, just take the new report code you are developing and -INCLUDE the same piece data preparation there. All that's left is perhaps performing some additional data manipulation (if needed) and finally creating the actual report.
It should be relatively easy to do depending on how structured your code is. Of course, make a good backup before
Prod/Dev: WF Server 8008/Win 2008 - WF Client 8008/Win 2008 - Dev. Studio: 8008/Windows 7 - DBMS: Oracle 11g Rel 2
Test: Dev. Studio 8008 /Windows 7 (Local) Output:HTML, EXL2K.