Looks small enough to fit in the stock location possibly
http://www.abspowerbrake.com/electrichppage.html
The new Electric High-Power Master cylinder Kit from ABS Power Brake was recently awarded the title of Best New Product at the 2005 Hotrod and Restoration Show at Indy! This new technology features a totally electric hydraulic system that offers the highest pressure and the smallest system in the automobile after market industry.
The new system can be retrofitted in place of the master cylinder in most American cars. The unit requires no vacuum and does not require a belt-driven pump. It features only three small components that can be mounted on the firewall or hidden under the car, for either under-floor or swing pedals. This is a 12-volt electric high power master; Our competitors are only 10 years behind!. This unit has a built in accumulator, if engine stalls pedal can be applied 20 times before you lose assist, then is back to manual brakes, never losing the brakes at all. This modern Brake system in two convenient sizes 2”x10” and 2”x 8”, that features all key components in one attractive housing. Our 10-59 presentation is a Power booster, master cylinder, metering/proportional valve and even a hydraulic stop light switch. Small space BIG reward, the unique shape and good look, allows to be located on the firewall and is unique for frame mount; this master piece should be the heart of all modern brake systems.