I believe the screws on top are a 5/16 hex head sheet metal screw, 1/2 inch long. You can use a nutdriver to install those. The original screws did not have a screwdriver slot.
The dash is fastened to the sides of the cowl with a angle bracket. Bracket is fastened with 9/16 inch hex head bolt with fine thread and special washers. Its the only place on the whole car that uses those type of washers.