They may not actually be "3-Rail trucks". Remember that WAY BACK in the 1960s, or earlier, 2-Rail scale wheels did NOT have the current RP25 NMRA wheel profile with a more prototypical small flange, thus 2-Rail wheels had a pretty large flange, however not near as big as the "Lionel pizza cutter" flanges. Whenever I find those old 2-Rail trucks a 2-Rail swap-meets or shows, I try to buy them as they work quite well on my Atlas O 3-Rail track & turnouts.