I would guess that extra gear motor on the leadscrew is to change feed rates since it doesn't have a QCGB. It won't work for threading, but for anything else it should be fine.
Were you able to get the spindle apart? If you're only disassembling it to change the belt, you can get lace up flat belts. As others have said, it can be hard to get apart. The rear nut requires a pin spanner. The large bull gear has a set screw and a key. To get the main bearing off the spindle, you'll need a much larger hook spanner, but I can't remember the size.
This is a good group and others here will have many more answers for you than me.