67 to 74 disc brake conversion, PLEASE HELP!!!

p.s. still no pics of the brake assembly but was wondering if anyone would be able to help me with this, the guy I bought my dart from said that it was the original 273 engine in it but after talking to a cpl of guys I know everyone seems to think that the motor is bigger than the 273 here is a pic of engine (not the best pic but any ideas)