Do what makes you feel good, no big deal
a 7/8" to 15/16" (no bigger bore) appropriate MC,
& a good adj. proportioning valve, proper distribution valve for 4 wheel disc
stainless Teflon inners/lines, so you don't lose any pedal,
from rubber hose expansion
& adj. prop. valve to help with the proper brake bias,
it won't hurt the car or the value
albeit front disc & rear drum is adequate, the RR & Super Bees had big drum brakes
just not as good IMHFO
do what makes you happy, I don't ever build by committee
if it's not an OE resto, or big $ #s car, then who cares if it's not 100% OE
just use quality stuff
I do still like 4 wheel disc.,
especially if you have to replace worn out or bad old drum brakes
especially when I like spirited driving up here in the sticks,
far less fade with discs, especially going downhill...
I will eventually do it on my 68 RR too, it will probably be manual brakes too
(SSBC is what I have on the shelf, done a couple sets of them on other cars)
but with discs on all 4
(may do an electric booster, if needed)
You need to watch out for wheel clearances, a lot of discs set ups, front or rear
just won't clear offsets or inside rims, without grinding on calipers etc. or spacers

in old 15" wheels (15" min. is a given if you do, do it), depends on what wheels you have
good luck, have fun with what ever you decide