Yes. We are also evaluating the M340. Upper management prefers AB since we have standardized our treatment plant on it. With Open Sockets AB should support it, although it would be better if they implemented it like they did in the ML1400 as a checkbox.
If you are considering a Gateway module ProSoft released a new PLX31-EIP-MBTCP unit that will support Modbus TCP/IP to CompactLogix for less than half the price of the MVI69 modules you may have looked at... http://www.prosoft-technology.com/content/view/full/16509
This could be something to consider if you don't have the 220K of memory for the RA sample code posted above, or if you are considering using a gateway solution for an 1769-L16 processor.
I downloaded the application code and the ModbusTCP Slave works without modification. If this could be turned into an add-on instruction it would be perfect. For what I am doing I can work around that for now. I have looked at gateways but I need to keep the costs down on this project and this is the best solution for me. Thanks for all the information you all provided.