Started with a 3" length of 0.25" X 0.375" steel cut from a 12" length with a hacksaw. The ends were cleaned up in the mill. One corner was located off the end and the side. The mill was then moved 0.250". The hole was center drilled, drilled with a #21 drill bit, and tapped 10-32. The process was repeated 5 times along the length of the work piece.
The holes were not that even using this process. Probably should have marked out and center punched. Maybe also start with a smaller drill bit to minimize wander.
The stock was thinned to 0.188". It was turned sideways in the vise and the mill was set to a depth of 0.071". Cuts were taken (10 - 15 thousandths) bringing the side down to 0.082". This was repeated on the other side. Marked every 1/2" between holes and cut at the marks with a hacksaw. Cleaned up the ends with an end mill, filed and retapped to complete the tee nuts.