1956 Mercury. As you can see in the photos, the brake booster somewhat dominates the space under the hood. I can't even remove the valve cover without first unbolting the booster.
Disks on front, original drums on rear. What can I do to take less room and improve on this arrangement?  

Is the MC/BOOSTER part of an aftermarket kit? If so, can you give the vendors name and PN's ?

Do you know or can measure the booster diameter?

How much additional room do you think it needs (booster) to remove the rocker cover?

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The car is in Australia now, but the brakes were upgraded in CA back in 2018. I can't see any identifying marks on the booster or MC. However, the invoice quotes 5474009, which appears to be a very common booster code. And NMC1481 which I'm guessing is Napa Master Cylinder and again, 1481 seems to be a common MC code.
The main booster body diameter measures 8" but that increases to 9" with the flange. The flange only clears the valve cover by about 1/2", an extra inch would be nice. Of course if the whole (smaller) unit was flush against the firewall, that might help also. And then I see the Wilwood setup with no booster and wonder if that is an option.

I have a set of those Valve Covers, too.  I love them...

You'd gain the most room if you went to manual brakes, but I'm sure you thought about that already. 
I just googled "thinnest power brake booster" and a bunch of skinny ones popped up- they probably work the same way- build vacuum and just help out.  You'd just have to adapt your Master.

7” dual diaphragm boosters are fairly common. In my limited experience they don’t make as much boost as the larger units. If the car has power steering, there’s also hydroboost units available. Check the Mustang resto mod sites. And the electric ones, I’ve only seen adds and references, never actually held one.

Many of the front disc conversions for the early birds use a dual master with the old oem remote booster on the front disc only. Same unit that did all 4 drums originally. Not cheap, but there are some aftermarket units available.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Does your booster the the bracket and linkage at the rear as shown in the lower illustration - 

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Summit part# OER-B10518 for 66-70 Fairlane or Torino which raises the booster 3". I did the conversion on my 56 Victoria and does what you're trying to accomplish. Great look and lots of clearance all around it. You'll only have to elongate 2 of the mounting holes less than 1/16"

SE Wis

Thanks all,
I've considered manual, but am not confident in getting it to work.

Kultutz, I have the adaptor you show. Vacuum is down a bit, around 15, but that will hopefully remedy with some other work being done.

Dave V, The current bracket gives a lift of about 2 1/2", so not a lot of difference.

I reckon I'll go for a dual 7" and hopefully the flange is a little more compact also. The current setup looks a bit rough so a new one will at least will be nice and shiny.

You need a minimum of 18in HG for the booster, especially a dual diaphram.

Big cam? Did the car come though with power (TREADLE-VAC) or manual? 

How does the car stop now?

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Vacuum comes up to 17 or 18 with at about 2000rpm. I'm assuming my gauge reads correctly of course.
Just a mild cam. I can't be sure of original brakes but probably manual.
Car stops well currently. Not too sharp, not too soft, easy on the leg.