58 Rambler master cylinder swap????

I am desperately assisting an older friend on his 1958 rambler wagon braking issues !!! This car has great pedal feel and it totally fails to slow down and stop . Undriveable , scary !!!

All brake cylinders at the wheels are new , lines are new , hoses are new , it has no proportioning valve in the system . Original drum brakes all way around .Shoes are new .

             My personal concern centers around the fact that a Hot Rod mechanic installed a 2000 

Chevrolet S10 power brake booster and disc brake master cylinder on this car. Looks like a good professional install , but the car does not think about stopping!!

             This is not my car but I own a 1971 Javelin SSt and the AMC forum has helped me so many times and I thank everyone for the help. 

             This friend of mine bought this car out of Texas and was lied to about the condition of the engine and all. He is 78 years old and helps all his friends in so many ways . He is now in way over his head .

             I assume this car came with power brakes from the factory , the actual invoice is there and this was a 4900.00 car new!!

             Anybody out there have EXPERIENCE with this type of problem ??? I want to help this great old veteran and put a smile on his face again , The master cylinder I would suspect is the problem .

             Car did come with power brakes but was it vacuum booster ??? I do not know . 

             Please if you have seen this before please lend me a hand to make a difference in this mans day!!Many thanks , Joe in Tampa 

If someone put an S10 power setup on it, they probably did not know what they were doing, because it will solve no problem that that car will have. If it was hard to brake before, it was a repair issue.

I would bet the fabricator didn't do their homework on pedal lever length, pushrod length, master cyl stroke, etc. 

It would probably be easier to simply replace the power nonsense and restore it to stock.

58 was single-circuit -- was it also converted to dual? That would be easy on that car! If so -- or if you want to do that now, all it would take is to replace a couple brake lines -- use a 1964 master cylinder, which is cheap and plentiful, and exactly the same as 1963 (dual) except that the ports are a different size. I used $3 adapters to fit common 3/16" line to it.