My . 02 worth;
I believe it takes just that to operate your PS pump. Then, quite possibly another 3 to 5 HP to operate the mechanical lift pump. Then you factor in the parasetic loads of the engine like other elements such as alternator, oil pump and then enter wind drag,tires etc. etc. (read John Holmes article) and you quickly learn that it's much more like 3/4 times that just to move the vehicle under it's own weight across a flat surface a 40 MPH in 4th gear.
Has anyone had the oportunity to use a machine that measures HP via a hand cranked generator? To produce a steady 1 HP, you have to be long winded and have a pretty good arm.
Try to operate your worn out mechanical lift pump just by moving the lever.