When I was a little boy, sliced or chopped shoulder were as popular as pulled pork, and properly cooked.... sliced shoulder is highly under rated. Your plan of holding (even chilling) before slicing is a good option. All the intermuscular fat which has broken down during cooking will firm back up and allow you to make good slices.
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This diagram will give you an idea of all the muscle groups, and help you with the direction of slicing.
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Calling the 'blade bone' end of a Boston butt the 'bottom', the 'top' 1/3 of the butt contains the Coppa, tube and money muscles in the photo. The best slices come from this area and look like this.
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The muscles in the center 1/3, called 'loin' in the photo, are leaner... and the muscles around the blade bone are the second best meat, they might be soft enough to cube or pull into larger chunks.
In order to determine slicing direction, locate the money muscle end of the butt shown at the bottom of the photo below. The direction of slicing is from the money muscle toward the blade bone, and not left-to-right. The distinct 'tiger stripes' of fat in the money muscle show you the slicing direction.
If it's easier for you, cross-cut the blade bone end off (right at the end of the bone) and work with it separately.
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Your internal temps will be in the 190°'s but trust the feel of the meat when probing.