The Replicator and FlashForge Creator need additional support on the 5mm Y-axis shafts, so a popular modification has been to add additional bearings mounted in pillow blocks. However an item of discussion on the forums has been the correct standoff distance of the bearing from the rear or front panels. Apparently it can vary somewhat.
This version of a pillow block includes the OpenSCAD code, with a parametric setting to adjust the standoff distance to suit your application.
Additionally, I hate fiddling with loose nuts, so this incorporates nut holders which should simplify assembly. A 'washer plate' is also included to go under the exterior bolt heads.
EDIT 1/16/15: To my shame, almost a year later and I've not yet installed these on my own Replicator. And the reason for that is, that I've been sure I'd goof up drilling the mounting holes, and wind up with something that would bind, rather than support, the shafts. OCD prevents just drilling outsize holes. So, I've finally gotten around to making a drill guide. With this addition, you can be confident that you can get all of the pillow blocks identically and accurately (enough) placed.
EDIT 3/22/15: Finally, I have installed these myself on my Replicator, using the drill guide. The fit was actually perfect with no binding detectable.
Using the new drill guide:
See the photos. While presumably all Replicator and FF frames are cut or derived from the same basic CAD files. It would be a good idea to check the shaft locations. So first you place the guide on the side of the Replicator in a corner as shown. You should be able to 'bullseye' the shaft location in the larger guide hole. Make sure the guide is flat against the side, the top edge is flat against the top edge of the side, and slide the guide forward until the 'arm' just touches the inside face of the front. If the shaft is centered in the hole, then the center of the shaft is 28mm from the top edge, and 13mm from the inner face of the front.
If it's not 28mm from the top, you can change the 'shaftfromtop' parameter in the OpenSCAD code to match what you've got, and print another guide. If it's not 13mm from the front, you'd need to shim the pillow block, or adjust the height in the pillow block code.
Then, you just hold the guide in place at the left and right edges of the front and back panels, as shown, where it will mark the location for each drill hole. The holes will match the span of the pillow block and be spaced correctly from the top edge. Both holes will be 45mm from the side, which should just clear the y-rod holders. (The 'arm' serves no further purpose in hole positioning.) You can just drill through the guide and panel, or mark the holes for later drilling. A transfer punch is easily the best way to mark the holes. (A set of transfer punches is really inexpensive and you'll be surprised at how much you use them.)
Since the pillow block standoff distance is adjustable, this would actually be a good application for the Customizer. However, I dread seeing a bunch of "My Pillow Block" spam things, so I refuse to use it on principle.
The only other thing to note is that to shove the nuts into the slots, it's best to hold them with some needle-nose pliers, and shove them in such that one of the 'points' of the nuts goes in first - that's the only way they'll fit.
Otherwise, install just like either of the two ancestor things.
I printed at 0.2mm with 20% fill.