This one fits better.. But now the mains socket Won't locate properly because that part of the plastic is now 1mm higher and I forget to lower the part under the socket
In any case, the hex nut seems to work pretty well...

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Bit of a close shave next to the shifter box, so need to take a millimetre off that next
..

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The infill of 50% does not seem to make them stronger than the 15% fill... It just took ages longer to print!
EDIT:
I have actually just realised, the rear holes are actually posts for the case fixings... So with this design those posts on the case would actually be too long... Though even if somehow the PSU bracket did look more like the original bracket, its only 1mm thick metal, and 1mm thick plastic isn't going to be very strong. So currently I am not sure of a solution for this.. It will basically have to have the posts on the case cut shorter and drilled to accept the bolt again..
EDIT2:
BTW if anyone wants to try this out so far.. I can send the current STL file...