I am not sure of the rules for adding a link to a post. This is the company that shows a booster/Master Cylinder as well as a front disc brake conversion using your spindles. Not cheap by any means but they say they have it.

https://www.classicdiscbrakes.com/51-56-Packard-Power-Brake-Booster-Master-cylinders_c25.htm

I have not purchased anything from them, nor do I have any connection what so ever with the company. Just passing along what I found. Bill

Funny you mention NAPA. I go in our local store a lot and live just a few miles from a major Warehouse for Napa. I already had asked about brake parts and they had all the wheel cylinders available in the warehouse for less than 10 bucks each. Wish that they had the Bendix Treadle-Vac unit. they had a listing for just a master cylinder but not the Booster unit. I plan to rebuild the brakes as stock to make the car Stop for now.

Thanks for all the responses. I agree that trying to do a conversion from parts would be costly and Still be a liability in the event of any failure. The system used by Packard was used in several makes of cars at the time and was engineered by Packard and I assume along with Bendix Corp. I agree that ALL of the brake components need to be replaced and that the E (parking) brake cables be working and the rear brakes kept in tight adjustment. Previous owner replaced wheel cylinders, hoses and lines but did not touch the Bendix treadle vac or the attached Master cylinder. I go to car shows and cruise nights see this system many many times. Hope to find a good rebuilder in the Chicago Area. I will look at Kanter as well. I have restored a couple cars in the last 35 years but this one is the first one that with just a few mouse clicks I can find parts and great information from groups like this. ( It has been quite a while. I will be asking Transmission questions as well.

I am a newbie to Packards, having dragged home a 1954 Clipper Panama. I hate to dredge up what seems to be a very hotly debated topic, but................ I am looking for any updates to this post, I have purchased a 65 year old car that currently has no brakes and as you know it does not matter how well it runs if it does not stop. for safety sake I plan to rebuild the system from the ground up. I cannot rely of what may have been done by previous owners. Likely nothing. If I am going to do any modern upgrades to the brake system, now would be the time. I prefer to keep the car stock BUT would consider a brake upgrade in the interest of Safety. I have owned and worked on several antique cars since 1981.
I have not talked to my insurance Company yet, which will be a factor in any decisions to alter the car from origional.
So has anyone done anything to their cars brake system that has not already been mentioned in the 7 page discussion? If so what? I see a company that appears to sell an entire conversion kit to the tune of $1500.00 for a total conversion. Thanks for any advice based on personal experience that you might have. Bill