Hi mtinn, welcome to the forums. I agree with what Capecoddersaid. your trying to build an index shifting system?

tell us just a bit more about what you are doing. did you get the bare frame? are you using 7 or 8 spd? depending on the age of the frame you may be stuck with 6 or 7 spd.

as for the shifters, derailleurs and freewheel/cassette as long as everything matches the number of speeds, ie 6spd freewheel, RD and shifter you should be fine. most pre 8spd shimano RDs will work with 6 or 7spd systems but one you get to 8spd plus it has to be the correct RD for the shifter speeds.

I hope I did not confuse you further