Transferred wall target 501 elevation to new location for better line of sight for the autolevel. I named it 501B
I mounted a scale vertical next to 501B (501B = -26.9mm below Z0 at BSC2, beam tube centerline) and centered the scales 300mm line with the new wall target horizontal line.
I set the autolevel zero on the vertical scale at 500mm (200mm above 501B)
Panning over to BSC2 to the elevation height gage, the scale mounted to the precision rod which Jim W. held against the ISI optical table surface, the autolevel zero read 244.0mm near to the south side of the table.
Note: the distance down from the ISI table requirement is 1661.7mm to the beam tube centerline. So height gage length = 1488.6mm [1244.6mm (49.0") + 244mm on scale = 1488.6mm] + 200 on wall target + -26.9 = 1661.7mm 

Results:

HEIGHT: AVERAGE FROM SCALE 243.45mm (244mm = PERFECT ELEVATION)REQUIREMENT +/- 1.0mm FOR BEAM CENTERLINE so the closer the better (<1.0mm ?)

LEVEL REQUIREMENTS: ACCURACY REQUIREMENT:+/- 100urads (0.1mm DIFFERENTIAL HEIGHT) 

SCALE READINGS:
SE CORNER: 243.0 RAISE UP 1.0mm 
SW CORNER: 243.0 RAISE UP 1.0mm
NE CORNER: 243.6 RAISE UP 0.4mm
NW CORNER: 244.2 LOWER DN 0.2mm