Well, I'll be back to edit this, but I'd probably go for:
A little short on anti-tank, but reasonably mobile, decent melee, and decent dakka:
Inquisitor Lord –Daemon Hammer, close combat weapon, Psychic Hood, sacred incense
Retinue – 3 Familiars, 3 Acolytes, 2 Veteran Guardsmen with flamers, Combat Servitor, 3 Mystics 198
No IC status while his retinue survives.
6 Grey Knight Terminators – one with Thunder Hammer and Storm Shield 291
Inquisitor with Psycannon and Emperor’s Tarot 65
Allied Callidus 120 – I’d’a made it five Seraphim with anti-tank pistols and grenades, but I don’t actually own the Witch Hunters Codex :I – I think that’d be a little over 120 – cutting a Familiar and/or an Acolyte should do it
2x5 <st1:place>OM</st1:place> IST with 2x plasma each 2x70; each in Rhino with XA and smoke 2x58
2xArmoured Fist Squad each with lacannon, plasma gun, veteran sergeant 2x101; one in Chimera with multilaser and heavy bolter 85; one in Chimera with multilaser, heavy bolter and improved comms 105
Leman Russ Battle Tank – hull and sponson heavy bolters 150
2xGK LRC 2x255 (I assume they’re erratad to carry Inquisitors – the other one carries the Terminators. Else, the Lord gets an LR designated transport, shrinks his retinue to 9, and picks up an Icon of the Just)