the worlord is here

[StainlessSteelCynic]

Personally I think it's a custom built chassis, I can't see it being built on either the M2 or M113 hulls because it's not as wide as either. That would entail some serious bodywork to cut it down from for example the M113 width (3m) to the Black Knight width (2.44m) as well as modifying the drivetrain components to suit the shorter and thinner Black Knight.
From the look of it, the hull is probably stuffed full of the engine, fueltank and drivetrain while the turret is stuffed with the electronics, sensors and weapon with very little space left in either hull or turret.