Magnum V belt conversion

Hi All,
I am converting a 5.2 Magnum to V belts , i have fitted the timing housing and pump from a LA318 i have which also has an alternator with a double pulley but no other pulleys came with this engine when i bought it. I did find locally (in Spain) a aluminum water pump (2 groove 6 1/2") and crank pulley (3 groove 5 1/4) that needs slight modification to fit. My intention is to just run with alternator/water pump and when its all running ok fit A.C. later on, power steering i'm looking at electric so leaving that for now so the third groove on the crank pulley will not be used i guess.

What would the normal pulley set up be with and without A.C. , is it single and double pulleys
Don't really get why the alternator has a double pulley.
V belt size, is it an 'A' 1/2" wide belt ?

Any photos would be helpful.