Questions on Install of Z1 Differential Bushing Kit

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In the midst of changing out the stock rear differential bushings with the Z1 polyurethane bushing kit. A couple of questions:
1. The stock front bushings have a relatively thin black metal washer that sits on the top of the bushing. Should these washers be re-used for the Z1 bushings or can they be discarded?
2. Exactly where should the rear Z1 bushing be positioned in the subframe? Should it sit flush with the backside of the subframe (i.e., the side facing the rear of the car) ... or should it be positioned so that it sits flush with the front of the subframe?
Thanks in advance for your input!