Actually, it's not the all-around weight of the roller. It's how heavy it is per sq. in. A taller roller will be quite a bit heavier...this is actually what you want. You can't go to heavy for something like this. (You ARE going to pull this with a tractor or something, aren't you?) Also, two things; Find out what the lumps ARE, exactly. If they are hard lumps of clay, it is possible they can be too large for the ground softness and not compact down into the soil. If it is good, wet, and soft under there, you may be alright. Or, if the clumps are smaller, you may be alright. One thing you can do, is after rolling, if you still have some rather large lumps, lift the sod, and break up the clod(s) with a shovel, and tamp back down.
Second, when you roll, especially with a heavy roller, make sure that your edges all stay tucked around the perimeter of the sodded area. Sometimes they can sort of fold up. I hope this helps. I wish you were near me, you would be more than welcome to borrow my roller to do it.
Thank you, Dad - for always being the dad that you were. You truly are my hero. You always were.