Shortest-proof-game challenge

Chat's been a little inactive recently.

How about a challenge: What's the fastest game you can find where white moves a knight to every square on the 7th rank, and black moves a knight to every square on the 2nd rank?

And an even more specific bonus: Without the knights capturing anything.

Starting from the initial array, how fast can you reach a position with White to move in which any of 15 white units can move to the same square? I looked at this a little bit and made a 62-move game that works. How much faster can it be done?

@6825

Shorter:

@6826

55

Starting from a legal position, here's one way this position could have been reached.

Very nice, good improvement on my first try.

@6828

53

Got bored this evening...

The positions are getting interesting. I hadn't guessed it could be done quickly with nearly all the white units on Black's side of the board. But it's not hard to understand after seeing it done. The promoted knights don't have as far to travel.

My first try looked more like tygxc's position.

I think 49 moves is the shortest for this challenge, which can be done with the square d5.

Since daStrwbrry's game was so much shorter than my first try, I looked for a related problem I might do better with. It may be a litle silly as a chess problem, but it's a challenge and someone might want to try it. It has an easy part and a harder part.

What is the greatest number of unmoved white units that can remain on the board in a legal position with White to move in which any of 15 white units can move to the same square? What is the quickest way such a position can be reached?

My first try this time gave me a 52-move game with four unmoved white units.

@6836

Yes, 4 units and 52 moves. E.g.

Non-unique proof game in 15.0.

How much can you shorten my first try of 27.5 moves for this position?

@6840

Shorter:

Another way to make it legal