When the Headstock is replaced, it will need to be realigned with the bed, so there will be time spent in clocking and careful adjustment.
Ideally, an Alignment bar would be used in the Morse Taper in the spindle (Use a piece of silver steel in the 3 jaw chuck. Do not rotate the chuck during this procedure)
Once the Headstock is aligned, you can fit the 4 four jaw chuck, clock the silver steel and when acceptably centred (As close as possible; within 0.0005″ would be my goal) and centre drill it.
Reverse the bar, and recentre, and then centre drill.
You now have an alignment bar which can be used between centres, to align the Tailstock.
Put the centres in the Headstock Spindle, and trim them (Top Slide set over by 30 degrees), before use.
The Tailstock centre might well be hardened, so not need, or be suitable for, trimming. The centre for the spindle should be soft, and so easily just cleaned up for use.
HTH
Howard