You "might" need a change in master cylinder bore to get a higher pressure in the system without the assist. Seems like you know what you are doing pretty much with brakes, just make sure you can achieve full lockup and then you will know if the pedal force is too high for normal driving.
I had an '86 spider for years and love it but decided to cut down to just 1 Alfa, so I only have my '72 GTV now. Same chassis, different body. Loverly cars!!!!! Nothing like the sound of the Alfa motor at full song. I also run big brakes; Alfaholics big brake kits.
Alfaholics 4-Pot Brake Kit