going back to manual disc brakes from power

I'm trying to determine if I have everything I need to go back to a manual master cylinder and the more I search, the more confused I'm becoming. My 73 Duster was originally 4 wheel manual drums and I had converted it to power disc/drum from a 74 Valiant. I still have the original manual brake pushrod but it appears that I may also need a plastic "spacer" plate that the pushrod bellows snaps onto? I also am trying to find a new rubber bellows and, so far, all I have located is one for $60!!! from Year One. I am hoping that someone has another source for that item. I'm also wondering how important the bellows is and what purpose it really serves. Does it help stop a fluid leak into the interior if the rear seal on the master blows? I'm converting to an aluminum 2 bolt master from Dr. Diff as I need a replacement anyway and I've never liked the feel of the power brakes. Thanks.