Lew,
The SH-10B3 (12kg) was the obsidian with rosewood base. The SH-10B5 was the obsidian-only base specifically meant for the SP-10Mk3 (round cut-out, 19kg). The SH-10B7 was the late 80s heavy (17kg) version which was meant for either the SP-10Mk3 or the SP-10Mk2A - quite like the SH-10B5, and almost as heavy (probably would have been if the cutout had been round instead of square). I do not know if there was something which made the SP-10Mk2A fit while the earlier SP-10Mk2 model did not.
The SH-10B3 (12kg) was the obsidian with rosewood base. The SH-10B5 was the obsidian-only base specifically meant for the SP-10Mk3 (round cut-out, 19kg). The SH-10B7 was the late 80s heavy (17kg) version which was meant for either the SP-10Mk3 or the SP-10Mk2A - quite like the SH-10B5, and almost as heavy (probably would have been if the cutout had been round instead of square). I do not know if there was something which made the SP-10Mk2A fit while the earlier SP-10Mk2 model did not.