Added link to first post and changed title to include the translated interview with the other significant MP designer Shogo Hasui, who worked on (grouped into their moulds & Japanese re-uses)...
MP-10 (Convoy/Optimus).... MP-10B (Black Convoy) (also to be used for BAPE and NGE soon)
MP-12 (Lambor/Sideswipe).... MP-14 (Alert), MP-12T (Tigertrack), MP-12G (Gen2 Lambor)
MP-13 (Soundwave & Condor/Laserbeak).... MP-13B (Soundblaster & Ratbat)
MP-15 (Rumble & Jaguar/Ravage).... MP-16 (Frenzy & Buzzsaw)
MP-17 (Prowl), MP-18 (Streak).... MP-19 (Smokescreen), MP-18S (Silverstreak)
MP-20 (Wheeljack)
MP-21 (Bumble/Bumblebee)
(did some early design work for MP-22 (Ultra Magnus), and worked on "Movie Masterpiece" Bumblebee & Starscream)

Hironori Kobayashi was the designer for these moulds...
MP-1 (Convoy).... MP-2 (Ultra Magnus, MP-4 (Convoy w/ Trailer), MP-1S (Sleep Convoy), MP-1B (Black Convoy), MP-1L (Last Convoy)
MP-8 (Grimlock).... MP-8X (King Grimlock)
MP-9 (Rodimus).... MP-9B (Black Rodimus)
MP-22 (Ultra Magnus)
(only worked on colouring for MP-5 (Megatron))
(Shoji Kawamori was lead designer on MP-3 (Starscream) with Hironori Kobayashi, but the modifications to MP11 were apparently done by Hironori Kobayashi)


Shogo Hasui has certainly been the most prolific with Masterpiece moulds/designs with about double of Hironori Kobayashi.

For the other three moulds not listed above, MP-5 Megatron and Star Saber were/are done by Hisashi Yuki, while MP-3/11 Starscream was primarily done by Shoji Kawamori.