I am in the process of setting up rear ls1s on my 69 camaro. I understand that you have to put a small spacer behind the backing plates in order to locate the caliper in the proper position over the rotor. ..Does anybody know how big the spacer should be? anybody set these up before? any help would be appreciated ...I know you can get them from BRP hotrods for $39.00 but that is what i am tryin to avoid