[d_ford]

Update....
The modifications were not done so I removed the rubber cup from the front master and the rear master was a little different, it was like you described with a thin rubber piece inside the brass part, so I removed it too. Now the rear master piston is sticking. I'm going to try to find a rebuild kit for it today or if one is not available I will order a new master cyl. I did get front brakes after bleeding them and they release now so we're on the right track. I'll update again after I rebuild or replace the rear master.