The 9 tooth-positions on the old style wheel are set at different depths with a special guage tool. You can tell if you have the old style wheel if all the bolt holes on the wheel are drilled the same distance from the rim of the wheel. I have a chart at my office I can fax you if you PM me with your fax number.
I have great results buying a cheaper variety of tooth on my old-style 1625: SQUARE "economy" teeth that use much less hp to cut through the wood. Obviously, they don't tolerate rocks as well as the round teeth, so there are trade offs.
Newer versions of the 1625 have spiral mounted pockets; I don't know the mounting instructions on those.