Model #s are located either behind the panel near the top of the handle or on the left rear of the deck. It would be best to have them. Your self propel issue may be a loose cable, broken belt or the list goes on. By cage , I assume that you may be referring to the guard that goes around the muffler? Metal colored and gets nice and toasty?

Yes, its actually model 20023. BY cage, I mean the black metal cover that gets hot when the mower is running. It would be nice if I can have some troubleshooting steps. Later this evening, I will try and turn the mower on its side to see the belt. Thanks in advance.

Torofan
You can download the free user manual for the 2023 here:
It has instructions to adjust the Self Propelled Cable.

http://lawn-garden.needmanual.com/1999-toro-20022-20023-20025-20027-20029-20061-21-inch-steel-deck-recycler-lawn-mower-owners-manual.html

So, I changed the drive belt but it doesn't seem like its driving the axle. When I start the lawn mower and lift it with the handle pressed down, I expect the rear wheels to rotate. They don't. Any idea what else I might look at? I opened the gear case assembly, but couldn't figure out what I am looking for.

I've had similar experiences with my Personal Pace movers. Sudden loss of self propelling has always been caused by the self propel cable breaking. I would suggest removing spark plug wire, tip mower on its side ( oil spout nearest ground ) have someone push down on the handle (all the way down) as if you were mowing and look at the belt. It should be very taught around both pulleys.If not then your cable may be broken or loose. Replace it if its broken - adjust it if it's loose. If it is taught you may have a gear box or other problem. Just a thought. Hope this helps.