As opposed to floor shift or column shift, one has plain over carpet hump, the other tends to have pre-molded base for the manual trans shifter. The auto doesn't have one but still features the manual hump, covered by the console. I used ACC Carpets. Since ordered direct, or at least who I used did, was able to request console brackets not cut, extra sides not trimmed and the dimmer switch hole not cut. Perhaps it wasn't anyway for 79-81, but being a 78 I was worried they might, mine doesn't have one in stock location. I was also offered the pressed vinyl mats both sides for a fee, which I perhaps should have accepted, but had floor mats anyway. Point is, they are, or were, fairly flexible to customer requests. The carpet already comes with mass-backing for the high traffic areas, you can always add extra, especially vibration dampening insulation for the floor pan steel.
