Adjusting the temporary firewall with clamps so that it is centred over the plank, level, and the tip of the longerons will be 23″ above the plank.
I ensured the 23″ height from the plank to the line where the top of the fuselage sides will be. The temporary firewall was centred to the plank and leveled using a plumb bob.
Once these criteria were met then 4 holes were drilled through the bottom of the temp firewall and into the 2x4s and screws inserted.