Good post! There are actually three versions of the side mirrors - the '96-98 (which didn't have heaters), the '99 (which was the same shape as the '96-98 but was available with heaters), and the '00-02 (which were the new shape and available with heaters).
When I was upgrading my '97 to heated mirrors, I was torn between the '00+ and the '99 versions; in the end, I liked the looks of the '99 better on my truck.
That limited my junkyard searches quite a bit - a single year ('99), in white. Took forever, but I finally found a matching set
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1997 4Runner Limited 4WD E-Locker ~200k | Falken Wildpeak A/T3W 265/75/16 | Pro Comp 69 16x8 | OME 2906 | B&M 70264
Addicted Offroad Front Bumper | Spiker Engineering High-Lift Hood Struts and Ultragauge Mount