Nick- You are correct, the carbs will not clear a power booster. I have manual brakes now but will at sometime go with a hydroboost set up:
http://www.hydroboost.com/ I want to put a air box (ram air set-up) over my 3 webers so I will need to move my master cylinder outward 1 1/2":
http://www.twminduction.com/airbox.htm Spin Tech mufflers
http://www.spintechmufflers.com/ I have had my Firebird since 1980, but did not try the 6pac till 89' and stroking it 1 1/2 years ago.
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-HOT OHC