So assuming you're doing a dually conversion to your 1500?
8 lug (whether 2500 or 3500) spindles don't directly bolt to 1500 control arms, upper ball joint is different. You could redrill the bolt pattern for the ball joint but since the 2500-3500 upper arms are better (forged) just swap to those. They bolt right onto the frame.
8 lug rear axle bolts right in as leaf spring width is same 1500-2500-3500 but what you have to decide is how you're going to solve the width issue. Semis won't fit between the dually fenders without changing something; some run a chassis cab rear because it's narrower but that will involve some other work as the width between spring packs is narrower, or some widen the dually fenders, etc. What kind of suspension setup you plan to run will come into play too, bagged, static, lifted, whatever.
Richard