Final position:
Lower bound for shortest proof game :
Note
1. that each black N must have entered its respective corner before the nearby P can move.
2. that the Ks cannot enter their final destinations when the Bs are already there. But something must shield the Ks from the Rs. Therefore the Rs must be one square further away and the white Ns be in between Ks and Rs. Once the Ks are in the Bs can follow and then the white Ns can move on and the Rs take their final positions.
with that in mind we find that
overall white moves are limiting
on top of that there is a "tempo" constraint in the beginning becaus black has to make 9 N plies before the two Ps can move
we'll need at the very least the following white plies:
11 plies to move the K from e1 via b2 and h6 to g8
1 ply to move the P
4 plies for Rs: Rh1-g1 and Ra1-b1-e1-d1
17 plies for Ns: We need to move a N to d1 but Nb1-c3-d1 does not work because the of the following necessary sequence of evens: N has to leave b1 to allow Ra1-b1 which is required to allow a black N to a1 which must happen before Pb2-b3 which is required to allow the white K out which must move through c3 or waste two plies. But if the N moves from c3 to d1 to make room for the K it will prevent the black K to enter via b2. Therefore we know that getting a white N to d1,e8,h1 and a8 will take at least four plies each, plus one because of parity.
5 plies to get the Q from d1 to h6 (Qd1-c1-b2-g7-h6 is not possible because the Q has to leave b2 before the white K can move out but may not enter g7 before the black K has moved out)
4 plies to get the B out (to let in the black K) and back
Total: 42 white plies or 41 1/2 moves
Proof game (still one move too long, B makes one extra move)with minimal number of moves:
1.Na3 Nc6Nc3 Na6 2.Nb5 Na5Nf3 Nc5 3.Rb1 Nb3 4.Nh3Na4 Na1 5.b3 Nf6Nh6 6.Ba3 Nh5Ng4 7.Bd6 Nf4Ne5 8.Qc1 Ng6Rg8 9.Qa3 Rg8Ng6 10.Kd1 Nh8 11.Kc1 g6 12.Kb2 Rb8Bh6 13.Kc3 Bg7+Kf8 14.Kd3 Bc3Kd4 Be3+ 15.Ke3 Kf8Ke4 Kg7 16.Kf4 Kg7Qc5 Kf6 17.Rg1 Kf6Qh5 Bc5 18.Be5+Kf4 Ke6 19.Kg5 Qf8 20.Nd6Rg1 Qg7 21.Qb4 Qf6+Re1 Qd4 22.Kh6 Rd8 23.Ne8Ng5+ Kd5 24.Qh4 Kc5Ne4+ Kc6 25.Nf4 Kb4Nf6 Kb5 26.Re1 Qa6Kg7 Kb4 27.Kg7 Ka3Qh6 Qc4 28.Nd5 Kb2Ne8 Ka3 29.Ne3 Qa3Nc3 Kb2 30.Nd1+ Kb1 31.Kg8 Bb4Bd4 32.Bb2 Bc3Ba3 Bg7 33.Bc1 Bg7Bf8 34.Qh6 Bf8Nf6 Qa4 35.Nf6 Re8Ne4 Qa3 36.Nh5 Qa4Ng3 Re8 37.Ng3 Qa5Nh1 Rb8 38.Nh1Ne3 Qa6 39.Ne3 Qb6Nd5 Qd6 40.Nd5 Qc6Nb6 Qb4 41.Nb6 Qd6Rd1 Qa3 42.Na8 Qa3 43.Rd1 *