More efficient ac pump?

What's the difference between the C171 and the Sanden? HP draw-wise.
This is an 80s truck which would have had a C171 to begin with "if it had come from the factory with air" which it didnt.
I have no problem with the RV2 on my old Fury. but because of the size and clumbsiness, I wasn't wanting to go there on this truck.
I did look on "Classic Air" (or was it "Vintage air"?) and they say that they have AC compressors that only use 5-6hp instead of 15-20. I'm not sure what model compressor they would supply/ or if it might work with factory AC hoses, or evaporator, or condenser.
from what I see, what they offer is to retrofit what they have in place of an RV2.