I have 4 wheel drum brake now in my 1970 dodge challenger. How hard is it to put a brake booster in? Do I need a different master cylinder? Where can I find one?

A booster does not so much add braking power as it does reduce pedal braking effort (downside is it reduces braking "feel"). Are you having a specific issue (as is) that we might be able to address? Or were you going to power discs?

it isn't that hard.
I believe for your car all the factory pieces are repro'ed now.
Dr diff carries it all I believe.
even though they are cheaper, I would steer clear of stuff like master power brake and their competitors.

I have gone through 3 different boosters and about to go for a new 4th.

I hear you should stay away from the ram man too. but no personal experience. just what I have read here.

personally I would get a booster for a 1979+ dodge magnum. these boosters had provisions for a 2 bolt aluminum master cylinder. if your converting anyway, might as well convert to the best option. you will also need the pedal linkage under the dash. its different between the manual and power disc cars.

if you're really adventurous, step up to hydroboost.

The drum brake MC push rod hooks directly to the brake pedal, the PB booster hooks to the pedal through linkage...you'll need the linkage and a different firewall reinforcement plate in addition to the booster.

I did this to my 67 in the pic.. NOT a E body but here is my add..

I had a parts car, a 66 coronet, with power brakes so I had everything.. Biggest difference was the linkage for the power brakes was like the pic above, with a bell crank.. The NON power was a direct rod into the master cylinder..

The support plate was the same for power or non in mine...

I cannot tell you any difference as I never drove the car with its NON PB system ( it was a field car I towed home).. Booster Dewey rebuilt the booster and told me that it was the "single" diaphragm unit....

Hope this helps......

My '70 Challenger came with 4 wheel power drums. It would stop right now at lower speeds around town... almost touchy. At high speeds, initial bite was strong but not much endurance plus uneven.

Power brakes take a different pedal linkage with less leverage and less travel so that needs to be part of the plan.

If you are wanting power 4 wheel drums, you can piece it together with used parts, AP store booster and master and/or parts from vendors like Dr Diff.

I would and did make the front disc conversion at the same time to get better braking vs drums. Also, comparing researching parts and maybe some trial and error, I would go with a matched kit.