The 1084s don't have "auto centering" any adjustments must be made by hand... 
The only reason for the picture being chopped off would be the tube used itself, a PAL tube can display 625 lines while an NTSC tube can only display 525.
So while it's easy for a PAL tube to display a full NTSC picture an NTSC only tube will most likely crop the picture as it can only really display 525 lines unless the monitor contains some scaling circuitry... 
You are right about the auto centering, none have that. I meant the verticle, it auto centered between NTSC and PAL. Never had to touch the adjustments. On the D2 I had to do that as it was severely chopped off at the bottom by like 3"!