4 wheel disc brakes

this is the email SSBC sent me when I asked about the dist block and an adjustable proportioning valve and switching from rear drum to disc later. I think this answers your ? about the simple way.

"with rear drums right now, you will need SSBC adjustable proportioning valve A0707. Install it in the line to rear brakes, and adjust as needed to avoid brake lock up. you can connect the front brakes directly to front bowl of master (farthest from firewall) and rear brakes directly to rear bowl, nothing more required except the proportioning valve, which can be readjusted when you install rear disc brakes.."