Very interesting. From Malaysia we actually know Gnatholea subnuda Lacordaire. But this item is completely different and, in my opinion, undescribed. Do you only have photos, or did you capture specimens ?
The seize is not out of range; G. subnuda is a smaller item indeed but other Gnatholea species (from Vietnam, Laos, southern China) reach larger seizes. Your pictures show a male (strong developement of the pronotum and mandibulae).
If one day you meet this species again, don't hesitate and collect them!!