An old thread but I seem to have a similar problem - did the discotech conversion using

10.87 rotors
72 Ebody calipers
1 1/32 master
all new lines and hoses

No proportioning valve at all....

10*1.75 drums out back of a 69 Plymouth Belvedere.

Not a super firm pedal, car stops but can't lock up anything, felt better with the manual drums!

Where should I start?

Plazomat