Finley played light at about 240 lbs. last year. A tall man at that weight isn't going to knock down many NFL front 7 players. MM's comment to Finley when he came to camp last year was, "What, we're not blocking this season?" Then again, you'd be hard pressed to find a stud TE blocker who runs routes out of x, y and z as Finley does.
Vernon Davis wasn't much of a blocker early on, got better as he went along, but now he's looking pretty lean and a little chippy...keeping the speed up as age sets in one supposes. There are trade-offs.
Finley has packed on some pounds coming into training camp this year according to some reports. Maybe he's committed to blocking improvement, in keeping with wanting to show he can be all-around in this contract year. We'll see. And we'll see how the added weight affects his speed.