The big bolt cover will be nearly flat, so a pickup floormat will not fit right. I've posted pics of the floor in my 1964 GMC 4000. Transmission is SM420. Highest part of cover is 1 3/8 inch higher than the floor next to it. If the cover from a pickup is used, it might need modified since it will be about 5 inches higher on the shifter and may not allow full forward and back movement of the shifter.

Pics of the floor: http://rides.webshots.com/album/577354545JHpFxI