[LH Lead-Foot]

Your vacuum leak under the dash is engine vacuum leaking past the atmospheric
control valve. Pushing the pedal, closes an internal valve to apply engine vacuum to make the booster assist in adding pressure to the brake master.

Removing the vacuum line will remove engine vacuum from the booster, so yes, you will have no vacuum leak.

It is time to make a decision on a replacement booster and master cylinder. These are safety items and not to be left guessing if they will work or not, unless you are in a farm field only and not on the streets. Double diaphragm booster of 10 - 11" is normal for excellent assist and the master cylinder if questionable should be replaced together. Master cylinders are very cheap. Just make sure you brush on the bench top bleeding procedure and if lucky, you may not have to bleed the 50 year old lines at the bleeder valves. If not sure, check them as well before making you entire parts list.
Try Rock Auto and the highlighted part number for viewing the list of vehicles this part fits or used on. Usually accurate.

Depending on past service, but front, rear brake components, plus hoses and metal lines are required to complete assessment on the entire brake system.
Other wise, a new master and booster won't help much but to expose other parts near failure.

Just get into the habit of replacing these parts every 50 years or so. I am picky on brakes, backing plate wear behind rear shoes, high temp lubricant and calipers (If Equipped) lubed to float properly, including the pads fitment within the holding frame so they are free to move.

Just plan on a booster and master...that will get you started.
ASE Master Tech since 1978 / Retired