I've purchased a new higher speed rear end from EDL services for the '35 1200, and the shop doing the work is telling me there is some amount of grinding needed to get it to fit the case, so I've told them do that carefully. They are telling me that even after the rear end is installed the original rear end was shimmed up and the concern is the shims needed for the new rear end would be different. Is there likely a source for the shims or would these need to be made?
Are you speaking of the shims used to set the rear axle shaft end play? If so, I found no source for them and just cut mine with scissors from steel shim stock.