FYI, someone else drilled the head tube on the limited edition titanium Birdy and add the Brompton luggage block:

(courtesy of Google Translate)
"I actually dismounted the fork (very simple on the Birdy with his Aheadset headset reversed), then precisely drilled two holes, added inside the socket head a curved plate of titanium reinforcement (from a piece of titanium tube that distributes the stress over a large portion of the head socket) and outer side a piece of aluminum profile to the same dimensions as the front block bracket of the Brompton frame and drilled for the two fixing bolts.

I had previously measured the thickness of the head socket of the Birdy Titanium which is in fact already quite thick, it is manufactured by CNC machining of a titanium block (for memory this Birdy Titanium was produced only 250 copies, for such a small number, Pacific Cycle has manufactured several elements of the frame by CNC machining thing that they probably would not have done for a bicycle produced in series).

Do not weld on a hydroformed aluminum frame heat treated like the current Birdy, not only destroys the paint but it loses the heat treatment and thus weakened the frame.
Before making the change, check that the Birdy Aluminum Steering Bushing is sturdy enough to support the weight of the front bag.

One more thing: if you look closely at the picture, you will see that on my Birdy fork release lever above the front suspension block is very close to the unlock lever block Brompton.

It will be necessary to verify that there is no interaction between the two on another model of Birdy because Birdy titanium even if it looks like the other Birdy is a completely different bike, everything was re-developed by Pacific Cycle for this model: other main frame with asymmetric main beam, any other rear suspension arm with folding adapted to exploit this asymmetrical tube, front suspension fork that uses the same concept but also redesigned."
https://www.bromptonforum.net/t2502p...elos-parisiens