Ok, well I think based on my own research, the lead screws I will keep for now. It seems the more pressing issue is the spindle. I have to figure out exactly how I'm going to fit a properly sized motor in this little area. I'm no machinist but I have a few tools, I know how to tap holes, so maybe if it's just a matter of an aluminum bracket or two, this won't be so bad?
If you look at the pictures you can see what I'm working with. The wheels and the little rubber band looking things make up the existing belt drive. It slips easily so it clearly has to go. Here's kind of what I'm thinking...
I'm going to use a dremel to cut out the portion of the gantry where all the wheels are. I'll make a large square flat section where I can thread some screws for some kind of bracket for the new motor. So it will sit pretty much on top of the lead screw, and a short belt will connect it to where the spindle head currently is... which I guess I will need to change out. Is there a good guide for setting up a short belt drive? Like with teeth so it doesn't slip? The reason I was thinking a belt, was because there isn't much room between the spindle head and the Z axis.