I really like what Brook and the Printrbot team did with the carriage arrangement on the new Printrbot PLUS 2.1, but was saddened there was no conversion kit!
Anyway, here is my homebrew one with my heavy duty extruder block.
This extruder block has done hundreds of hours of printing with no issues whatsoever.
I don't have a BOM for the whole lot, but it's coming soon. You will need a selection of M3 and M4 screws. I've used socket head cap screws but anything will be OK. You'll also need a spring for the tension on the extruder lever.
Anyways, this bring the benefits of a DRAMATICALLY lighter carriage assembly (the only real weight is the bearings and the motor), along with mounting points for a fan to cool the filament in the area where the drive gear is. This tends to be a huge point of failure with the stock PB extruders.
You can easily mount my LED light strip plates to the fan too (see my other designs).
So when you disassemble your old carriage, put the LM8UU bearings into the printed bearing blocks, then bolt these on the inside of the carriage.
Add your extruder to the top (the original laser cut wade's extruder will fit perfectly too).
Add your belt to the belt mount and to the X motor side of the carriage.
Mount the new carriage mounts to your carriage ends.
And you're done. I hope this makes sense. When I get a BOM written it should be a bit easier, but if you're good with tools, you'll have NO problems working this mod out.
EDIT 1 - Fixed spelling errors