I assume since you are rebuilding the injectors yourself you have had bad experience with buying rebuilt injectors. I had a bad experiance when we, (me and my dad) rebuilt my moms 300td. We decided to replace the injectors since their pressure was out of spec. We got rebuilt injectors. Some of the rebuilt injectors were leaking and a few were under the specified opening pressure. When we exchanged 3 of them, one of the newer injectors still leaked a little bit. Since then I got a box full of bad injectors from a friend. The springs and shims are good in them. I have had to service one injector on my 300d and this time I did it myself. Since the nozle was good I just shimed the spring. The injector sprayed like new after that.
I would like to let everyone know that if you need to get injectors serviced, take them to a shop that knows what they are doing. Otherwise you are just throwing money away.