Hi Woody,
If you can find bits for automotive, or industrial use it should be cheaper, easier than anything custom made, I've only retro fitted a brake servo once, that was on my old Cox GTM using S brakes and the remote Mini servo that would be fitted under the passenger side dashboard.
If I were doing this in darkest Africa where I live, for an accumulator I would probably use a a refridgerant gas refill bottle normaly thrown away when empty but pressure rated and fitted with a shut off valve, a Tee piece could be fitted to the tank shut off valve, suction side fitted with a none return valve to maintain your vacuum, T'other side connected to the vacuum side of the brake servo,
Industrial compressed air fittings from Norgren, Festo, etc would supply quick connect Tees, couplings, nylon hose, all light weight and easy to fit.
The locaterfield hillclimb car (no idea of the driver) was all hand control with the clutch servo on the tunnel just behind the gear lever but looked to be a one off, not a manufactured item.
I think there is a dissabled drivers association, they should have people with this kind of experiance who can advice better than us able bodied
John

Hi Woody,
Contact - British Motorsport Association for the Disabled
www.bmsad.co.uk
The objective of the British Motor Sports Association for the Disabled is to assist drivers with disabilities to compete in motorsport.
There will be people who have done this before
John

Thanks John
Didn't know they existed!