Update 1/4/18: New version available! (Anet A8 Titan Aero Mount v2 w/ inductive sensor mount)
I upgraded my Anet A8 extruder to the E3D Titan Aero extruder/heatsink/hot-end combo. This design puts everything along the X axis on a horizontal path. I've attached a picture of my setup so you can see what the finished part will look like.
At this thickness, the parts are highly rigid (even in the PETG that I printed them with) and should be able to stand up to the same level of abuse as the original steel carriage.
In order to keep from having to print supports, the carriage prints in 2 pieces. Because of this, there will be additional thickness over the factory carriage.
You will need 8 M4x10mm screws - the original M4x8mm screws are not long enough to go through both parts and into the linear bearings securely.
I've also included the STL file for a new fan duct, since the fan has moved and typical A8 fan ducts will no longer be that useful. The biggest reason I moved the fan is because the big extruder gear changes the depth of the carriage quite significantly. Note: with this fan duct, you will likely have to adjust extruder temp (mine's about 3 degrees different) while it's on because it does blow over the nozzle a bit
0.4mm / 0.25mm layer height
Note: I printed with PETG, use whatever layer height you typically use for structural parts.
Use at least 4-6 shells to improve part strength as well as multiple solid top/bottom layers.
Part fan being used will improve strength as well.
Infill percentage is up to you, I printed at 100% but anything above 20% should be just fine.