As Fabs says you need UM522..
This is a new part.. and comes with a Shorter Stub axel so you do away with the washer that you have to use in the standard kit and the worlds rear end kit.
I bought a set of shafts from rdvg on ebay part no. LA245 which had the shorter stub axle on the shaft (this is the same shaft you find o an FS) you only use the stub axle.
When i fitted the shorter stub axle to the worlds rear ended RB5 shafts i have, it made the car narrower... but if you have the new gear box set with the wider plastic suspension holders or the UMW514 and UMW515 blue ally wider suspension holders then this will push the car back to width..
I cant see why the proline axle wont work? You just need to put the stub axle part to the drive shaft already on the car..
Hope this helps
Nick