Update August 14th, added the LM8UU version, although I have NOT TESTED it. Also I included a picture showing how the level arm is NOT solid, rather is has a shell of support material that breaks away really easily.

Update, March 10th, 2015: updated minor parts of the assembly and added some final parts (z adapter for the optical switch, pin for the extruder lever arm). Added pictures of it in action. One of the best I think I've ever made. Eveything worked on the first try. Switching from a 40x40mm fan to 30x30mm made it fit much better and interfere less with the frame. Make sure to use a small screw with the z optical switch adapter (or use the minimalist one that just pushes on).

I'd love to hear input! Mines working great. I've printed Taulman Tritan and PCTPE, gold and silver PLA, Polycarbonate (still trying to get better adhesion - best I've gotten is with kapton with abs-juice at 110/280/45 bed/hotend/chamber)

Intro:
I wanted to print PLA (and nylon, PC, and flexible filaments) with my unlocked Davinci (luc's repetier firmware is great!)

I designed a drop in replacement that only needs some M3 hardware, an MK8 extruder gear, a 624 roller bearing, E3Dv6 hotend, and 5V fan (30x30x10 for the E3D itself, or 40x40x10 for print cooling with a permanent 12V power source for the E3D fan).

I made it so you can use the original brass sleeve bearings (I know they're not the greatest - I'm making a version that will use LM8UU's) but this minimizes bought parts.

Just print the carriage, extruder and accessories (belt clip, opto trigger, extruder arm, fan shroud, and fan connectors, board mount - sounds like a lot but it all fits on one plate) and should fit great. The brass sleeves fit well and can be tightened if your tolerances are better than mine.

You'll need to transplant the board from the original extruder - just wire up the fan, heater, thermistor and extruder the same way from the board.

As far as software goes, I'll be adding a version that uses an MK7 gear that should work with the stock extruder calibration, (maybe without any firmware changes!) but for now you'll need luc's repetier firmware with the following changes:

" #define EXT0_STEPS_PER_MM 165"

I've had issues with this and I just put M92 E165 in the start gcode

DO NOT change thermistor type, it is a 104gt-2 i the stock and e3d, but the temp table is custom for their resistor values.

"#define MAXTEMP 305 // to go up to 30"

"#define MAX_DEFECT_TEMPERATURE 325 //increased as well"

And finally you'll need either:
a 5v 30x30x10 fan instead of the e3d 12v fan
or a 5V 40x40x10mm fan for the print cooler

Davinci controls fans with 5v so in the original config, the same 5V just controls the e3d fan. If you want a fan to cool the prints, you'll need a 5v 40x40x10 fan so davinci can control it. You'll also need to change near the beginning of the configuration.h:

" #define REPURPOSE_FAN_TO_COOL_EXTRUSIONS 0 //Setting this to 1 will repurpose the main Extruder cooling fan to be controlled VIA M106/M107 "

Set this to 1 and davinci will control the print cooling fan, but you need to find a permanent power source for the e3d fan (12v for stock or 5v if you got one)/