Small brake boosters

My dad is building a 57 chevy and is having problems finding out which brake booster to use.The car is set up with discs in front and drums in the rear. The one we have is 11 inch and it looks like the exhaust is too close. Does anyone know what chevy has a smaller booster that we could use.Thanks

CORVETTE HAS 7"

http://www.kugelkomponents.com/

They have all kinds of neato-bandito stuff.