Brake mods??

You do what you gotta do to make sure the fronts lock first.
Nothing else matters much beyond that. Do what you gotta do to make that happen. There is NO certain part that will make that happen. Those wheel cylinders might be enough or they might not. Depends on your tires, your front brakes, your master cylinder, your weight distribution, your skill as a driver, road conditions, your fiber intake, etc.

Drive it CAREFULLY on a smooth wet road and hit the brakes? Rears lock? Start adjusting your proportioning, change wheel cylinders, move battery to trunk, whatever.
Fronts lock first? You're probably fine.

When my dart was stock, I had an incident where I was passing a school bus on a foggy morning, because I'm brilliant like that.
Dude in oncoming traffic decided he needed turn on his headlights since he was driving a white car and he was even more brilliant than me. I mashed the brakes, and my Dart swapped ends and I slid backwards off the road.

It's a real problem. At a minimum, I'd splice in the prop valve and dial the rears back. Hell, take em off. They are just glorified parking brakes on most cars anyway. Save changing wheel cylinders until you've got the rest of the system built. Massive binders up front can make it a non issue.