It's actually not that odd of a Combo since Lousaka Polite was a LB coming out of college as well.
Larsen was a LB from Arizona when he came out in 2008.
The transition from LB to FB in the NFL is fairly common. Think about it, linebackers and fullbacks basically do the same thing on a running play, now you just flip the responsibility.
A quick google search of "linebacker turned fullback" plus a couple of random memories yielded me this incomplete list
*Robert Thomas of the Cowboys was a LB turned FB who replaced Moose Johnston
*the Cowboys currently have Isaiah Greenhouse
*LB/FB Darrell Young, the current Redskins fullback, is a converted linebacker.
*Current Vikings FB Ryan D'Imperio
*49ers fullback Bruce Miller (once touted as a passrush prospect)
*Brit Miller--current Ram, former Panther
*Spencer Havner of the Packers has been used in this role. Maybe it's a Spencer thing.
*Aforementioned Polite
There are lots of linebackers turned fullbacks throughout the NFL and college. This is a very common transition.