Letters from Max and Leo

What Ben Bitdiddle Dropped

Ben Bitdiddle dropped this as he left the theater. Maybe you can make something of it?

Go back to where it all began. Don’t leave the building.

1. Number of horse heads plus the number of beards.
2. What goes here.
3. What’s missing.
4. Digit following “Gift of the L. I. S.”.
5. Maximum flow 600 GPM _.26 H20 of this.