You will need to get the BB frame mounts so the engine sits in there right. You will also need to modify the heater box to the big block style as well as get a bigger radiator. The radiator support should be cut out to fit the BB radiator so it gets more air flow. If you use an HEI dist. you will need to get the small body type or massage the firewall some to get the stock HEI to fit. You will also need to check valve cover clearance in relation to the brake booster. A BB car will always bring more than a 6cyl car even if it is not original. You will probably want 3:55 or 3:73 gears in the rear to get decent performance.