The oly time you will actually need the adjustable PHB is if you go wider on the rear tires/wheels. I don't know how wide the Y2K wheels are, nor the tires that you are going to mount on them,,, but if the wheels are wider than 10 inches and the tires are bigger than 295s,,, I can almost bet you need an adjustable PHB.
Some cars, due to production tolerances come from factory needing the axle adjusted to be centered. Once you lower it, it could get better or worse depending on which way the tolerance stack up. Mount the tires up and find out is bout the only advice I can give.