Hey Dumb Asterisk Asterisk Asterisk Asterisk,
It will work, probably. The 82 to 85 had a slightly different set up with different front calipers and proportioning valve and mounting brackets and the MC/Booster is different from pre 82 to 82 to 86.
I have had different master cylinder / booster arrangements over the years including from a Toyota Kijang and mostly they will bolt up with a little work and then I find the actuating rod is no longer the correct length to match the brackets and pedals and have to cut and weld the rod. OK, so at one time I was sufferring from front lock up but that was cured by going to a 1981 CJ setup.
HOWEVER if you are going to go non standard you may as well go the whole hog and put on the double diaphragm YJ booster and Mastercylinder, look up threads on here about brake upgrades.
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE