For those of you who've done a power disc swap how'd you extend the pushrod???

[Baketown Scotty]

I'm having some issues with my brakes and think it may have something to do with the geometry or just length. 1969 Blazer, 10 bolt front with disc, 14 bolt rear that I just switched to disc. Switched to mid 70's MC and have .20'' between MC pushrod and contact point in MC. As far as I know its a stock booster. What dimensions do I need on the rod between the pedal and the booster? The clevis in engine bay from booster is tight up against the firewall, is that normal or should I have a gap? What dimensions should I be looking for? Bench bled MC. Trying to bleed lines and can't seem to pump up any pressure. Tried bleeding with a partner. Also attached a clear tube to each of the 4 bleeders and taped them to side of Blazer so they reached above MC to try and get all air out. Just can't build up pressure. Suggestions?