I'm sure those machines all have 3-phase spindle motors. If so, then the answer to your spindle speed question is just a matter of putting them on a good VFD (Variable Frequency Drive). This will generally allow you to double the max spindle speed by over-speeding the motor.
If your existing servo motors are working, there's no reason you can't continue to use them. All necessary conversion parts needed to use the existing (I assume analog) drives and resolvers are readily available from pico-systems.com, and others.
On the quill drive - those heads look quite different from a standard BP head, which is what most quill drive conversions are designed for. Designing a quill drive is a fairly straight-forward undertaking, the only really hard decision being how to attach it to the head. Some use the four tramming bolts, others, like the Elrod, attach to the lower flange (where the lower end of quill feed-stop screw attaches), and to one or more of the covers near the top of the head. On mine, I went with an approach I've yet to see anyone else use - I slipped a 1/2" plate between the head and the belt drive housing. This was very simple, very solid, and required no modification whatsoever to the machine. (see pictures below, with covers removed). The other trick is making a rigid enough connection to the quill itself. This is always done by attaching a yoke to the bolt that attaches the "eye bolt" for the quill stop. The design of that yoke is tricky.
Regards,
Ray L.