This was a pretty difficult position. I knew there was some kind of sliding puzzle with the pieces in the bottom ranks but it wasn’t easy to resolve it all. Eventually I managed to make a 113-move proof game which reaches the position, but not without breaking the 50-move rule.
Here's how to avoid the 50-move rule. Same retraction sequence to get the Black Bishop to g1, then a quick un-promotion of Bf1 to reset the counter.
This is really a Retro, not a Proof Game, so I stopped retracting after unpromoting bQ on a1. The rest is easy.
This was a pretty difficult position. I knew there was some kind of sliding puzzle with the pieces in the bottom ranks but it wasn’t easy to resolve it all. Eventually I managed to make a 113-move proof game which reaches the position, but not without breaking the 50-move rule.