Ok, so what is a "low boy" truck?
IIRC, these are 70-ton roller bearing trucks with 28-inch wheels used primarily on triple-deck auto-racks. (Or not?)
Low-deck flats... doesn't matter if a bi or tri level rack is placed on top (or a Vert-A-Pac

) They're not standard trucks with 28" wheels, the sideframes, bolster pad, etc are also modified (as too how much Exactrail did may be another story)