Hi, as a matter of interest, the headstock is a design criterior in itself, totally different to normal centre lathe requirements.
A centre lathe is a universal machine in it's material processing needs, which means that apart from four jaw chuck and faceplate work the main feature is the ability to handle lengths of material through the spindle bore, but not necessarily for production requiremnents as in a capstan lathe, but more for longish spindles and drive shafts.
In this mode there is no bar feeder present to steady a long shaft, more often than not there is just a bush or three screws to centralise the shaft at the end of the spindle bore.
Given that you may want to make parts on a repitition basis from bar material, then the bore in the spindle must exceed the largest diam the collets can pass, (32mm) this means the bearings must be large, and if you want to run ally or plastics then 10,000 rpm is not far off the list, and bearings for a spindle with a 6mm wall will need to be about 45mm bore size and be able to handle 10,000 rpm.
You will also need a bar feeder to get the material through the chuck, and this will HAVE to steady the bar as it rotates at 10,000 rpm or the whole machine will go into orbit.
The other side of the coin is if you only want to make parts from precut billets then the bore size becomes irrelevant if at all.
The bearing configuration would be as per normal spindle practice with two angular contacts in "O" configuration at the chuck/collet end and a pair of axially floating radials at the other end.
All of this could be contained in a cast ally headstock housing.
Drive would ideally be three phase VFD with polyvee belt drive to the motor, or direct driven if spindle positioning is a must.
Ian.