Need REAR END HELP haha

[bguild]

Okay guys.. I am not a gear head yet but need some help here.. I just bought 68 chevy step side.. SWB
The guy converted the front to disc from a 72 truck. The front wheels are 5 lug and the rear still is older from the original truck.. the rear is a 6 lug patterned wheel. I need to switch this out for a new rear end.. my question is what will work I WANT A POSI TRAC. I dont plan to make this thing a torque monster.. i dont plan to do any real serious drag racing I just want a cruising street rod. My question also is I would like rear discs would a late model rear end with disc work? If I am going to do it.. whats my best bang for the buck financially and performance wise???? Thanks in advance... also I think I might go air ride suspension.. and I have a ton of questions for that as well but lets just keep this simple to rear end help..

Also pictures of hot rear ended women are allowed as it will help my creative thought process.