S13 struts can be redrilled, if done properly, its safe. Its common practice to do so as the s14. s15 struts are longer. You can either use a 14mm drill bit or a 9/16".
If you can find them seperately, its possible to just press out the ball joints for the knuckles, and use the matching ball joints, as said before s14/15 are different.
You will need the new master with the 32 rear brakes, and possibly a new booster, although it might not be worth the hassle, what has the ceffy got on the rear atm?