Bell is as raw as raw can be. He may be athletic, but he's a late bloomer coming from a microscopic college program, and has zero meaningful NFL snaps.
Walker is big and slow. He's more of a guard, really. If he's playing at LT, Joey Porter is going to have legendary games and I doubt Belichick or Ryan won't exploit the open-door policy with a huge grin on their faces.
Remember, some fans here say Peters was the worst LT in the NFL last year, yet Walker stayed on the right side and Bell stayed inactive all season last year. Now, they are the answer?