I would put the strikers on before I sanded and painted. But I am interested to see how you go about this one.
If doors are on... you could try:
obtain some art clay or use wax. Roll into ball, place in door latch so that it protrudes enough to slightly rub door jamb. You can apply a thin layer of wax or other white residue substance (crisco for example) to the jamb. Close door and slowly push to the point of the door latched position. (or you could put some lithium grease or vaseline on the wax)
The wax or clay should leave a track and stopping point in the white residue on the jamb.
You could also take some pre-measurements and make a preliminary mark in pencil - then compare with the wax/grease method just as a double check
Hopefully strikers will be adjustable within 1/8" or so
Good luck
DJs74
I would try taping the door jamb. take a piece of side walk chalk and shape it into the shape of the striker with a point on it. lock the chalk into the door latch and close the door gently. might take a couple of pratice runs but with patience it would be possible.