I thought disc brakes required a brake booster. When I converted my fronts to disc, the instructions said my setup required a brake booster for the for the front discs. I guess I assumed that was universal for all disc brakes to get enough squeese out of the calipers. Also have the proportioning valve set up.
Seems to me, if your going to convert to front discs, to save some cash and get the right setup now, unless it's going to be a long while before the switch.