Clan 'mechs were original, except for the IICs like the Marauder IIC (Gulag), Warhammer IIC (Tomahawk) and Rifleman IIC (can't remember it's Macross name at the moment) which were just Clan updates of standard Inner Sphere 'mechs.
The most famous 'mech lifted from Dougram was the Battlemaster (can't remember it's Dougram name though).
Ahd the Phalanx did make it into Battletech, but not as the Naga... All Clan centric designs were original, IE, Hellbringer (Loki), Timberwolf (Mad Cat), Stone Rhino (Behemoth), Dire Wolf (Daishi), the Naga, etc... The Phalanx became the Longbow (IIRC). Also, the Spartan was used too as the Archer.
Vostok 7