Back in the day (mid-70s) vacuum brakes were an option. They required a vacuum connection to the tow vehicle, and I wouldn't want to try to tie into a modern tow vehicle's vacuum system because you'd probably make the computer system angry when pressures weren't what it's programmed to expect.
I believe they were discs... if so (and if the disc system is still installed and working) you could probably convert that to a modern electric/hydraulic disc system. Unless someone else has replaced the axles since that trailer was new, though, you may need new torsion axles anyway, and probably some new parts for things like flex hoses, etc. So, you'd need to decide what kind of brake system you want, etc.
Zero Gravitas — 2017 Flying Cloud 26U | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill