Single to dual M/C. Some specific queries

Hi all, I know this subject comes up, but I have found contradictions at times. I’m in the UK so really need to order the correct parts just once.due to shipping and taxes etc..
Car- 1966 Barracuda Formula S with stock10” drum brakes all round.
What to buy?
I’m thinking a 1967 master cylinder for all 10” drum brakes ( the easy part)
I want to use my original distribution block and am wondering what size plug I need to block off the rear brake port?
I assume new brake line from front of m/c to rear brakes?
Final query is which ports connect the front brakes from the distribution block. That’s really the part I need to get right as the shop doing the job need to know.
Thanks for any help, after a low mph brake fail with the single system I never want to be there again