Jim Harbaugh ran a run-heavy version of the West Coast Offense. He'd have a fullback playing in the backfield at least half of the time. David Shaw still uses a fullback to this date with that same offense.
We're running more of a K-gun type offense, but now with a heavier emphasis on a balanced attack. In previous years, it was a similar offense, but with a higher pass to run ratio. Friday's game was pretty darn close to a 50/50 mixture of run / pass.
It's actually less of a classical "spread" offense than most other spread teams, and inching closer to a pro-style K-gun offense that Jim Kelly ran back in the Buffalo Bills' heyday. Ian Book progresses through his WR1 through WR3 or WR4 reads, and then takes off, whereas with most spread teams, a quarterback usually does a WR1 and WR2 read, and then takes off running, unless WR3 or WR4 is obviously wide open.