As far as i can see, you dont "have" to have the distributor
in. It does make it easier since you have all marked to be in the same location. But if you dont it is not hard to relocated the distributor.
Although i am not very familiar with the 3.1L, I am assuming that if you are changing the ratio of the rocker arms you have to consider that you will have to adjust your timing, because if you increase the ratio not only are you puttin more pressure and wear on parts, but your duration of valve timing will increase.
Having said that this is a good and a bad, good because you will get more performace, bad because you will increase the wear on the head assembly(not enogh to wreck it or anthing really bad) but it is something to keep in mind.
I dont know if this really helps you, or you might know all this already, but someone else might benefit from this litle information.