You need to some serious thinking about this. To make a 502 Big Block, hell even a torquey Small Block, work you will need to build a good trans and rear end for the car. That peg leg you have right now will do nothing to put any serious power to the ground.
Like techinspector, I would suggest starting at the rear and building from there. How many miles are on the car? Have the front or rear suspensions ever been rebuilt? Good place to start if they haven't. Manual brakes are fine but you should upgrade to disc's in the front at if they're not there already.
Driveshaft will need changing as will the entire cooling system and exhaust. This is a big job and it will not be cheap to do it right.
Mark