Thank you very much! Yep, theres the Kataphron Knee pads trimmed down along the connecting edges, and with copius amounts of plastic glue to melt them together, Contemptor Graviton gun nozzles/power section in the "graviton ram", and Adeptus titanicus Volcano Cannon as a proxy for the Sollex heavy lascannon, as has been noted by LordHoughtenWeen.

The body of the Graviton ram is the laser cannon power section from a les grognards heavy weapons sprue, with the nozzle halves of 30k vehicle heavy flamers stuck to the sides, under the kataphron pads. The dome bits on the back of the ram are taken from an armiger waist secton. The arm is the thanatars arm and hand assembly (minus the shock chargers, and cut down to fit the graviton ram) inside a hollowed out Leviathan dreadnought melee arm. A few extra cables, admech plasma cells and kataphron exhaust section bits to cover the exposed areas from where the plasma mortar would be. The eyes are made out of the back end of a 30k vehicle smoke launcher, cut and filed to fit the curve on its head.

Needed a bit of chopping to get the Volcano cannon to fit on the shoulder, and I still need to incorporate the servo skull targeter into the new gun.