Hmm, I never knew that anyone is looking at that large code base ... so I assume, that you use OpenOffice (which is more or less obsolete today and delivers only 32 bit binaries) ? And not LibreOffice ? Have you changed that code from 2010 ?
So I further assume, that you want to switch the VASTPlatform to 64bit and due to that wish you can not work with OpenOffice 32 Bit (cross-platform OLE not possible).
Actually I am still working on LibreOffice 64 Bit (under C#), but we changed the structure of our large C# program. The original structure was, that we put all stuff into one big application - but over the years this became very difficult to maintain (we switched from OpenOffice to LibreOffice and later: 32 bit to 64 bit). Then we isolated all LibreOffice OLE communication into a different application (either 32bit or 64bit), wrote some code to exchange data between our large C# program and the "oowrapper" tool. The main application does the data fetching and prepares the data and started the "oowrapper" tool.
The result was a much better Ui experience (long task running). Have you considered to go a way like this ?