Need help replacing a flex fan with OE parts

[Prong]

I've decided to remove a flex fan the PO installed and go back to a safer factory fan/fan clutch setup. The truck is a 79K10 with a 350 and a SM465 4 speed tranny. It does have A/C but it's an aftermarket unit. I keep seeing different standard duty/heavy duty/severe duty clutches and it says the blade pitch needs to be XX inches in order to use the heavy and severe duty clutches. Also, I assume a thermal clutch is the way to go? Can some please suggest what parts and/or part numbers I should use?

[82Shortbed]

I suggest Severe Duty on the fan clutch.  From what my sales training at work told me.  Standard duty was 60-70%, Heavy was 70-80, and Severe was 80-90.  I'd say severe with 4wd and a/c. as far as blades go.  WOuldn't know what to tell you there.  yes go thermal too!