Faulk is a lock, I don't think it's even close. As a dual threat back he was perhaps the best there was in that regard. He could have lined up full time at WR. He had a 5 year stretch where he caught 80 or more balls in each season, and he topped 1300 yards rushing in 4 of those.
Marshall Faulk NFL & AFL Football Statistics | Pro-Football-Reference.com
Overall 7 1,000 yard seasons, 767 catches tops a lot of WRs already in the Hall, 12,279 yards rushing, 136 TDs.
Lock.