Nick,
Thank you. I see what you mean now.
I doubt I'd pursue a Precise cheekpiece top, the plastic part. Simply I suspect it would sit much too far to the left and wouldn't allow room for my face. The Precise is designed to go on hardware that's mounted on the right hand side of the stock, where the SG is mounted centrally. Although I could adjust it across, because the top is less tall, the hardware would be jammed into my face, rather than 1-1.5in below.
Making a spacer would be worthwhile if I had the Precise hardware, as the SG lacks in-position lateral adjustment, but not jyst for the top.