I went with power when I did my convertion as I was told disc brakes require more effort than drums. Although the man drum never bothered me. You also need to replace the pedal when going to power.
I went from drum to brake and just changed spindle out. I didnt even change the proportioning valve or master cyl and it is WAY better than the drums ever were. The wife still isnt allowed to drive it becuase of a power steering issue, but I would imagine she could handle it now.
I did the disk conversion up front and kept the manual setup. I don't think it is a problem at all. But then again it is pretty easy to press the brake pedal to floor when compared to my manual clutch...
With the proper master cylinder a manual front disc setup is more than adequate. I run a manual setup on my '68 with 13" front discs/10" rear drums and the pedal feel is excellent and I can lock all 4 with moderate effort...
I had the SSBC 4 piston front brake kit on my fastback, and it was more than enough to lock up the fronts when i wanted to. I have also had cars with a power steering setup, and it feels too artificial.