Torque converter help.

I'm new to the world of mopar and I need some help. I have a 75 duster with a 727 trans that is original to the car. I'm looking for a stall converter to replace the stock converter. My question is that the stock converter has the flywheel made on it and it is all one unit that bolts to the flexplate. The ones I'm seeing on jegs and summit are just the converter and you have to buy the flywheel separate. So if I buy a separate flywheel does that just bolt to the flexplate or does it replace the flexplate? Also will there be any clearance issues? I'm also aware that they are weighted and that's another thing I'm not sure about. Could someone just point me in the right direction on this issue. I have a mildly built 340 and I'm lookin for a 2700 to 3000 stall converter. Any help would be greatly appreciated.