Here's a picture of a 63 with a 5" channel and stock suspension.
http://s32.photobucket.com/albums/d41/coilover/ It has a flat floor so is similar to yours Five inches was chosen with the driver sitting in the seat and allowing comfortable head to top spacing. Be aware that everything mounted to the firewall/dash that has a certain spacing will change when the floor stays put and the cab is lowered. This includes the brake/clutch pedal assembly, accel bracket and pedal, steering column, etc. Of course the bed and core support must be repositioned so the front sheetmetal and bed match the lowered cab body lines. Channeling is not used as much as in the past because it's very labor intensive and so many suspension options are available to give one just about any stance.
