No one mentioned the front to rear bias control that is found on every dual brake Chevy truck I have looked at. On 67-72s it is on a bracket right under the master which is on the firewall. On 73 and later it is mounted on the front cross member, but it is the same for whatever year and power or manual brakes. I believe you'll need to use it. Because of the splitting up of your brake system you MAY need 3 pound residual valves front and rear because the master is as low as the drums.
Put a booster on this system and drum brakes will stop so fast they'll make your head swim!
As cletis says, it's a bad job and well worth the effort.
best wishes,
Les
