Hi Josh,
Brake proportioning valve for a rear discs roadster : the one from the Sierra donor is enough. If you want an adjustable one (knob), Rally Design sells the Wilwood one. It's a shame, because I could have send you one with the brake lines at a good price as we supply them too.
M10x1 brake T piece. members from the UK will tell you the cheapest supplier in your country I'm sure. I know Rally Design sells these parts too. Same than for the BPV, I could have supplied you one too.
M10x1 brake pressure switch : as a lot of us, I use the one from the VW Beetle, it is very cheap, easy to find, and fits perfectly. You can find it on ebay I'm sure.
Hope this will help