FWIW, if it was me, I'd sand them all down to match the shortie. I've compared the model image to a proto image, and the original fan ring height is just about dead-on. However, IIRC, the retrofit fans include an etched part that's added to the top of the plastic ring, raising its height slightly. I believe this should compensate for some loss in height, at least enough that only the most stringent scrutiny may detect a discrepancy.