Depending on who you believe, there are some 4WD Astro Van control arms that work with minor modification.
MY inclination is to believe that there's a genuine difference, and they're not truly compatible. However, some folks have installed them on a GMT400 and called it a success.
When this was me, on my '88 K1500, I just installed ball joints and bushings on the original arms. That's my recommendation to you, too. Ball joints can be any one of three styles--two sizes of press-in joints, and one flavor of bolt-in joints depending on the control arm. Bushings are available, two styles. One style can be replaced with readily-available Polyurethane inserts (or OEM-style bonded-rubber.) The fully-forged arms take a different Poly insert (I guess. Never done those myself) that's intended for a Hummer, I guess.
WHICH CONTROL ARMS DO YOU HAVE?