Pulley's and belts

You didn't tell us what engine you have and year. There were many combinations of accessories and pulleys, even in the same year, and sketchy info. My 65 SB isn't close to factory, but my belt layout works. I looked at many photos here and rigged up something. As I recall, my alt is alone (inner) and the water pump & p.s. share a belt (outer crank groove). I haven't figured how I will run an AC compressor yet.

I have a crank pulley from a later SB w/ 4 grooves, so seems that could support almost anything. I recall from an 80's car, so probably smog pump, etc. Cheapest way to serpentine is take the whole setup off a Magnum SB engine, but there are vendors who will take $$$ for a shiny setup. Personally, I think serpentine is less reliable. Many cars have trouble with them throwing a belt in the rain, or a non-critical component like p.s. pump disables the vehicle on the road (happened to me).