New guy with a new project

Welcome aboard. And of course we all hate you for stealing a great looking A Body like that! :)
You should have the 4" small bolt pattern on there now. Since you want to go to disc front brakes, the best option would be to find the upper control arms, spindles and calipers from a 73 or newer disk brake car. That way you get the brake upgrade plus the large 4.5" bolt patern. Check the "Car Parts fro Sale" forum here since there's always 73 and up parts to do this upgrade.
Also, right now you probably have the 7.25" rear end with the small 4" bolt pattern. Try and find a newer 8.25" rear end and you'll also get the bigger 4.5" bolt patern to keep things the same size front and rear. The 8.25" will easily handle the power of the 360.
And, as mentioned, right now the right side studs are right hand threads and the left side is left hand thread, so don't go all Hulk and twist off the left side studs, just turn them the other direction. :)

Good luck.