First off the motor they are selling is making 725HP on a motor dyno. That motor installed in a car, with all accessories will dyno around 600 RWHP. Vince made 560 RWHP for 1/3 of the costs, and it's a STREET combo. The above combo you mention is a RACE combo...
And yes, accessories and driveline will eat up a lot of HP, an average of 14 to 20% depending on the combo...