Mine came off of a Mitubushi Spacestar apparently they are the only ones known to have totally FLAT feet where it mounts to the roof, and therfore easier to fit...
I currently have a set of Mutsi cross bars ally ones which match the diag ones nicely and a roof box on top of that..
The only issue i have found with not using Vw ones is that they have to be fitted further in towards the centre of the middle line of the roof, which means that any roof box you fit will sit in a bit which makes loading and unloading a bit more difficult...
im not sure if the last owner fitted them or C-M-C who built it but i thing it was C-M-C Cheshire Moror Caravans, Mike apparently is a good bloke although after repeated attempts to try and speak to him since owning this bus have so far failed, but you might want to give him a rung or mail i'm pretty sure he could assist you..
See my van in readers rides team white [all the way by the way] and White Noise is mine or see June and May issue of Vw Camper and Bus for features on it all showing my bus White Noise with the bars fitted i aslo have some close ups if you want i will emal then direct to you as dont understand how to get photos up on here..
Hope that all assist somewhat let us know how u get on ..
Slanj
