Front mountings bolt onto two 'T' brackets which themselves are bolted to the frame. Looks like they use the crashbar mountings. Bolts through to the frame have spacers between the frame and the bracket, but not sure whether they are original part of the bike. Both sides have a round end 40mm in diameter. The length of the 'T' on the right side is 48mm, but longer on the left at 70mm.
Here's the right side
Here's the right side