Nothing illegal about that -- the truck light you used is tested and certified by its manufacturer as complying with all applicable provisions of FMVSS 108.
All these standards that you continually use to justify your argument sound like guidelines for current manufacturers,
They're not "guidelines". They're mandatory requirements. And they've been that way since 1/1/68. Periodically updated, of course, and replacement equipment for old cars needs to meet only those requirements that applied to the vehicle when it was new.