All three diaphragm kits D8R075, D8R076, and D16R2405 use the same voice coil part number.
(All three diaphragms have the same DCR specification regardless of any D8R versus D16R assembly number prefix. Actual transducer impedance will vary depending on diaphragm loading.)
Both D16R2405 and D8R075 use the same diaphragm part number. D8R076 uses a different diaphragm (dimensions).
All three kits use the same raw diaphragm material (.002 inch thick Aluminum).
There are also some differences on the diaphragm spacer rings used in each kit,
Information courtesy of JBL
Note that the D8R076 diaphragm assembly has also been labelled D16R076 in past years.