I am currently doing a rear brake conversion, but on a cinq I have so far found it quit easy, there are conversion plates on eBay, but the hardest thing to do is to decide on what brake discs and calipers you want on front and back.
I will be putting the standard front brakes on the back, calipers are off of an alfa 155,145 so on. The fronts I'm going for 277mm i think off an uni turbo not sure for definite
I will not be doing this but apparently you can keep standard 240mm discs and calipers on the front, and you can put on 227mm on the back but i have no idea what car there off or where to get them.