Brakes won't stop my Valiant 100

explain, in detail, "hard to stop". leave nothing out.

has anything been changed or modified: manual to power brakes, pedal, etx.

is the master cylinder correct for the application.

you're this far in, i'd replace the soft hoses and the distro blocks. if it's 69 you should the one with a prop valve/metering block/safety switch in it. that will at least eliminate another set of possible culprits.