not sure on BHP yet, Julian Godfrey is doing the engine, and the VR6 is unfamiliar to both of us, but with what we know 450 should be easily achievable for normal use with an extra 50-75 available for short periods. Should be ample, I hope, I know more is possible, but not sure it's needed. More importantly the torque figure should match, or exceed, the BHP figure.
In their day they only had about 275, but then they only had Mk 1 Escorts to beat, suspension and tyre technology has come on in leaps and bounds too, so I am optimistic.