Hi @rollypoli
Unfortunately, I do not have a way to convert the Allegro BRD database into Altium format.
For similar requests in the past, I have typically recommended using the free Cadence Allegro viewer. Cadence provides a free viewer that can open BRD files and allows you to inspect the PCB database directly.
Using the measurement and inspection tools available in the viewer, you should be able to accurately determine the placement and spacing of the connectors, mounting holes, and other mechanical features. This is usually sufficient to reproduce the board outline and connector locations on your own Altium design so that the new PCB remains mechanically compatible with the original board.
The free Cadence viewer can be downloaded from:
https://www.cadence.com/en_US/home/tools/pcb-design-and-analysis/allegro-downloads-start.html
While this is not as convenient as having a native Altium design file, it has worked well for customers who needed to reference an Allegro PCB layout and recreate the relevant mechanical dimensions in another CAD tool.
Regards,
Lukas