sunny booster is also an option. any of the relatively small boosters will still give plenty of pedal feel, id say on my car you have better pedal feel with the booster than without. As without the booster the pedal was just rock solid all the time and you physically couldnt get the car to stop anywhere near as good as it should. mind you that was with r32 brakes all round adn a 15/16th master
but i feel the booster made the car stop far better and gave you more feel for how much pressure you were actually applying

i also had landcruiser front brakes and r31 rears with a 7/8th master with no booster and that pedal was almost to stiff for street driving

but thats just me, im yet to drive a car that isnt running a booster that i think stops nicely. i like to be able to pull the car up confidently using just the force from my little toe on the pedal

13/16th master that will be a straight bolt in replacement will come from a datsun sunny, providing you already have a dual res master cylinder in the car currently. Easy enough to just go to a brake place and look through a master cylinder book. just look at the datsun ones from the 70s and 80s in the size you want. if they look the same as the ones you have now then there is a very good chance they will be a bolt in replacement