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Here's a mount that makes it easy to install a Duet (any version) to replace the stock RAMBo. It has a cutout for the V3's cooling fan. It is attached using the 4 screws that were used to attach the white pillars. Install this first and then attach the Duet with it's power connectors to the right (as you face the front of the machine).

http://www.thingiverse.com/thing:1992159