The mats for 3 spd and 4 speed are definitely different. 4 spd tranny cover has a hump that surrounds the shifter hole that accounts for the tower on the SM420 transmission. I've looked at mats from most of the big suppliers, and they only list one mat. See, the hump isn't a smooth slope like the 55-59...it's a rectangular sort of extrusion/stamping that creates a ledge. The problem with using a three speed mat on a four speed tranny is in fit. The three speed mat drapes over a four speed hump, and with a little bit of time, feet pressing down on that area where there is a void will cause it to tear. My old floor mats were definitely rotten, but I wish I'd have kept the pieces, so I at least could show you what I mean.
Thanks,
Hook
