The RepRapPro Huxley which I built almost a year ago came via the Indiegogo campaign which I believe followed the eMaker campaign for the first generation of this design in the summer of 2011. Since then, I noticed on the Wiki that the Y-carriage had been turned upside down. This is a great design improvement in my view as it provides a more stable support for the heated bed - less chance of 'wiggle' and less chance of the bearing holders breaking as a result of brute force and ignorance when removing printed parts.
When you turn over the Y-carriage bearing holders though, the nyloc nuts at the bottom are no longer captured - there is no hex hole to stop them rotating and tightening them can be a wee bit fiddly once the bed has been levelled as you need to use a spanner whilst holding the levelling screws still which is a shame after the time spent carefully getting the bed level - tightening the nylocs in this way can upset all the hard work!
The only change which I have made to the Y-carriage bearing holders is to place a hex recess to hold the nyloc nuts which take the levelling screws. You level the bed as normal but then only have one nut to tighten up to keep things tight - the one just below the spring.
To invert the carriage, you need to print out three of the reworked Y-carriage smooth rod clamps, one Y-carriage endstop holder/clamp and the Y-belt clamping components which are on the RepRapPro github and shown in the Y-carriage build instructions on the Wiki. You can then either use your existing bearing holders OR print out those which I have uploaded here which have a recess to hold the nyloc nuts as explained in the description.
As the prints progress, you will see that after the hole for the hex nut has completed, there is a point at which there is no support for the plastic which takes the M3 levelling screws above it before the second, (the original), hex capture hole starts. To avoid this, pause the print after it has completed the first hex recess and drop in a 3mm nut. (I use Pronterface when printing but used the Repetier Host programme to give an indication of where that was going to be so that I could get ready on the pause button as the Z axis moved up).
When assembling the Y-carriage, you may consider the purchase of M3 hex bolts to hold the Y belt clamp parts rather than using M3 screws or cap head bolts (the ones which take an allen key). If you use bolts with a hex head, you will be able to loosen and if needs be remove the Y-belt clamp in the future without having to remove the heated bed as this type of fastener can be released by using a spanner from the side - there is not enough space between the bottom of the heatbed and the top of the Y-frog to use a screwdriver or allen key.
One last point - I found my T2.5 Y-belt a tiny bit short to fit comfortably into the revised Y clamping system. I was faced with struggling to hold the belt tight over three teeth whilst clamping the ends of the belt together OR purchasing a longer belt - longer by 3 or 4 teeth. (I went for the latter - if you do the same, take care to purchase the 5mm wide belt as 6mm will not fit).