No matter what any one else says .... the only way to know which springs you need are to measure your particular heads to see what the installed heights are, period.
There are big block heads with no rotators.
There are big block heads with exhaust rotators and two different length springs.
There are big block heads with exhaust rotators and all of the springs the same
There are Big Block heads with Exhaust and Intake valve rotators.
There are probably big block heads with some other combination I have not seen too
Anyone who really works in a machine shop on a daily basis has learned that GM (and all of the others) have used so many different combinations of springs/rotators/ etc that the ONLY way to know is to measure. Period !!!!!
As far as the reason for the eliminators .... I cannot swear to it, but most performance applications do not need a crazy rotator under the spring, which is moving around too much anyway. The rotators are actually designed to keep the valve from wearing the seat in high load situations. Every time the exhaust valve closes, if it is red hot, it tends to "micro weld" itself to the seat. If you did not rotate it, eventually it would weld it self and come loose in the same spot so many times that it starts to erode the seat and the valve sinks into the head. The rotation itself is probably better for a mild engine, but once you start getting higher spring loads, and much higher rpm, spring stability is more important so the rotators should be removed.
Hope this helps,