65 GMC 1/2 ton brake line question

[CPO1]

Hey
I've read and I can't find the answer.

I have drum/drum. Currently, the line from the single master cyl to the front brakes is 1/4 but from the right front Tee to begin the rear, the line reduces to 3/16. Is that correct??

I am swapping the single master cylinder to a dual master cylinder with booster.
I question if I should run 3/16 all the way to the rear, or run 1/4 and connect to the 3/16 with a reducer. This reduced connection would remain at the location of the right front tee.

I suspect the PO (my deceased brother) altered the sizing back in the 90's when he restored this truck. At that time, he added a booster but kept the single master cylinder.
Thanks for your suggestion.
Cheers.