Actually turns out to be more like 4 feet.
OK, that's more than enough room for a dual band VHF/UHF antenna such as the Arrow GP 146/440.
It's a PITA working in a hot attic. Be safe up there. If you are unfamiliar or uncomfortable with attic work then you should find an electrician friend that could help you out. He could fish the coax down an inside wall and make a nice neat installation with no wires showing outdoors or running through windows. If you have enough length in the attic, also consider adding a wire HF antenna. Then the FT-857D becomes viable again. It's way more radio than any handheld.