in my 66 it was changed over to the sm420 4 speed and kept the low hump. a hole was cut and it banged out with a hammer, kept the orig mat. i have unbolted low humps and bolted in high humps several times with no problems. some of the big trucks like the c60's had a pretty flat pan with almost no hump because the cab set up higher. but i find things all the time i haven't seen before, so hopefully your will work with a easy exchange.