external oil pump

Whats the reason the chrysler hemi's I see have the oil pump on the outside instead of in the oil pan?

Is it merely convenience when changing bearings or is there more to it?

Is it a HP gain somehow?

 

The hemi was born with the oil pump outside the pan - Why it was designed like that, I do not know.
The race hemis simply use the stock oil pump placement - Much like the chevys running it in the pan until the point of switching to external belt driven pumps.

I do not know if an external gear driven oil pump is available for the Chevy? I think a saw an Arias/Fontana hemi running an Aviaid oil pump of the front gear drive - Maybe that would work for a Chevy too?