Power Brake Hell..... HELP!!!

If a later model booster will fit with your engine, buy one and install it.
Its shorter in length than your dual diaphram but larger in diameter.
I'm assuming you have the 4 piston KH front disc system and it does take a lot of fluid volume to make fluid pressure there. Proportion valve is part of that equation also. In all of this is reasons they were changed.
Still...you do not want the front brakes to lock those wheels unless panic stop extreme pressure applied.
I'll never forget the first front disc brake car in the family. Uncle Charlie's 62 Bonneville. A panic stop tried through everyone through the windshield.
That is for example of every brand having faults in their early disc brake systems.