Older LX and XT brakes, (as well as XTR), used to have the 4-pivot design which keeps the pads parallel to the rim as the pads move. But now the cheap b*st*rds at Shimano have dropped the 4-pivot design on LX and XT and gone back to the cheap fixed pad, (except on XTR). If I had the fixed type, I would find some New-Old-Stock or buy some used 4-pivot units.

(I actually have some 4-pivot LX brakes on a frame I just stripped for other parts.)