crankshaft/flexplate bolts

Hello,
Just got my tranny back from rebuild. I am piecing things together, so I never really had the flex plate bolts. I know the crank has (6) 7/16 I think fine thread bolts which are how long? My converter was built for the larger 7/16" bolts also and I have a B&M disc style flexplate. I was wondering if I use the 7/16" x 1/2" bolts here. And is that the same bolt that goes into the crankshaft? I know these have a special head on them which is very thin for clearance. I also was wondering if these had any washers involved? I know MP sells a set of 6 7/16 for the crank and 4 5/16 for the converter. where can I buy the larger 7/16 bolts without spending the cash for a set which includes the 5/16 that I do not need. I remember on another car having one of the flex plate bolts backing out and making a real noisey racket. Thought my car was going to blow up. So I really want to be sure I do the right thing here regarding sizes and washers if necessary as well as torque specs? Any info on this would be really helpful,