I just did my ‘37. I bought the bushings and bolts. Some suppliers have the whole set with shackles only, others let you buy just the bushings, tapered bolts and rubber if your shackles are usable. I bought the AD shackle set for my rear that has shorter shackles and they were identical except for the length of the shackle itself (just to lower the rear a tiny bit. My shackle in the rear was egged out… so your ‘39 parts will fit if they are in good condition. Prices can vary considerably on all parts. Here’s the list I keep and shop from.
Jim Carter (oldChevytrucks.com) chevsofthe40s.com fillingstation.com classychevusa.com bowtiebits.com classicindustries.com iandireproduction.com 38chevy.com hotrodssheetmetal.com chevysupplyofassonet.com earlychevyparts.com speedwaymotors.com Classicparts.com https://newportwipers.com/ www.vintagepartsclub.com
www.steelerubber.com americanclassics.com and lmctruck.com have limited amount of pre AD parts but do have some. Mar-k.com https://directsheetmetal.com/collections/chevy-pickups https://windshieldframes.com/

Larry
Old man᠁Old truck᠁neither one goes very fast. All you need in life is TIME, PATIENCE and MONEY.
If you are missing one component, you'll need an abundance of the others two.