70 Dart manual brake to power brake swap

Sublime Swinger said
Personal preference mostly for the piece of mind to update to today's braking power. I also think it would look alot cleaner than having that conversion bracket that come with some of the kits nowadays, would rather use Mopar parts as replacement than buy one of those kits.

But I would need to remove the firewall studs and make some sort of backing plate to bolt it to correct?

This is a misconception. Adding power brakes does not necessarily increase braking power. It reduces pedal effort, which is not the same as increasing braking power. A-bodies are a little unique, the pedal ratio does change slightly because of the linkage needed for the power booster (because the booster has to sit higher for clearance. The factory made up the difference in ratio by boosting pressure with a smaller master cylinder bore. But, without a change in ratio or master cylinder diameter the booster just makes the pedal easier to push, it doesn't make the brakes do any more.

I have found on my cars that a manual disk set up with a 15/16" master (same diameter as an A-body power brake master) gives better braking feel than any of the stock power booster set ups. I actually converted my Challenger to manual disks from power after driving my manual disk Duster. Even on the larger E-body I found the manual disks to be an improvement in braking feel. I wouldn't add the stock power booster to any of my cars.

Here's a picture of the booster from a '74 Dart, it shows the stock booster and A-body linkage that's needed...