It's not the 8hp loss we want to see, it's the proper operation of the bolt on parts when the engine is supplied. If you want to get the water temp right, hope you have the water pump and more importantly the pulleys (ratios) the engine is going to ship with. The radiator is the next big problem but obviously that's not for the engine builder to get setup.
Another big builder had their pulley ratios off and cooked a bunch of engines ... this was because one of their suppliers changed the part and the engines were dyno setup with the electric pump and then before going out the door the other parts were added (also resulted in leaks in the car due to bolts not torqued properly and never tested while running). It's great to ensure no leaks on the engine dyno before getting in the car right?
Other items like
oil pumps should be tested on the dyno beforehand as well right? That's why I like to see the final setup as much as possible if the engine builder is supplying those components.