We took off both the differential and wheel axles today in preparation of our new sprockets and chains.
The largest sprocket on the differential for the wheels was a challenge to remove. We didn't want to directly hammer the sprocket and gears to avoid damaging the teeth on them. Thus, we tried everything from wedging wood in between to sandpapering the sides. After much maneuvering, we were able to get all the parts off.
I hope to clean out the dirtied insides and grease/oil the chains and gears some more before assembly tomorrow.
I read further on the physics of rowing. There's quite a lot of resources out there.