Updates at 23/10/2017
I just noticed that my Y Rod Holders have started cracking. It will still take them a few days or even weeks of use to break apart. However, I'm pretty sure it happens because I printed all the pieces with 20% infill (awful choice). I would recommend (for extra stiffness) 35-40% (in case of PLA). Other than that, it works perfect. I have it running with RAMPS an Marlin (so it's more a Prusa i3 since the moment when the original board died) and managed to push it up to 90 mm/s. Normally I print at 70 or so. I keep the stock direct drive MK8 extruder.
This is my version of AM8 frame. Some pieces have minor changes, are reinforced, or have room for washers. The most important changes affect to Y rod holders, whose M3 bolts now point inwards to avoid colliding against the bed bolts. The Y motor holder can be positioned so the bed male connector doesn't collide against it. Also changed the Y Tensioner in order to make it more sturdy. That leads to the need of changing the LCD location, which is placed on top left corner of the gantry.
608ZZ Pulley: https://www.thingiverse.com/thing:2251246
X Tensioner: https://www.thingiverse.com/thing:2243372
Y Tensioner: https://www.thingiverse.com/thing:2459058
Z Endstop Fine Adjustment: https://www.thingiverse.com/thing:2249275
127 Gantry Assembly Jig: https://www.thingiverse.com/thing:2464467
Y Tensioner Assembly Jig: https://www.thingiverse.com/thing:2578992
Y Motor Holder Assembly Jig: https://www.thingiverse.com/thing:2579064
X Axis Printed Pieces: https://www.thingiverse.com/thing:2466306
PSU IEC Switch Cover: https://www.thingiverse.com/thing:2236965
Reprap Discount Smart Graphic LCD Display: https://www.thingiverse.com/thing:2631178
Improved Y Belt Holder for Stock H Plate: https://www.thingiverse.com/thing:2631145
Pieces currently on progress: [16/09/2017]
-LCD Front Plate (it used to be a 2.5mm thickness plate, but I have reinforced it to rest on the LCD PCB. I have to test it myself yet)
-PSU Mount V1 (works perfect, but I'm still thinking of something a bit more rigid)
-Board Mount V1 (same than previous one, although my board died so I'll be uploading this piece for RAMPS too)
-MKS Mosfet Case (works perfect, but it could use less material and be more similar to the two previous mounts...)
Within these weeks I'll spend some spare time in order to create a detailed BOM, but feel free to print the pieces in the meantime. The extrusion-related hardware is pretty similar to the original design, though the printed-parts-related one changes a bit, but it's not much of an issue in money terms...
-40x20mm B-6 extrusions 440mm (2 pieces)
-40x20mm B-6 extrusions 340mm (2 pieces)
-40x20mm B-6 extrusions 320mm (3 pieces) [the original AM8 says 313, but the original bars stick out a little bit from the right side]
-M5x6mm button head bolts (20 or more)
-M5x10mm socket head bolts (60 or more, I would buy like 100 to have spare)
-M5 T-Slot or M5 square nuts (eBay worked nice for me)
-M5 washers (as many as M5x10 bolts, though there are optional, I like having them between bolts and printed pieces).
-M3 bolts (12, 16, 20 and 24, will update about how many of each)
-M3 nuts (plenty of them)
Some of the pieces are quite obvious to position to be printed, some are not. I'll write a tutorial, but feel free to ask anything in the meantime