What inlet/outlet size mufflers?

['70 C/10 SS500]

My '76 500cid Caddy motor is getting ready to find it's new loving home in my '70 SWB truck. If I use midlength headers, what size head pipes (dual pipes, exiting at rear of cab door out the under/side) should I use and what size should the inlet and outlet i.d.s on the mufflers be? Mid-lengths are about the best headers commercially availible (that I know about) for the big Caddy motors without having to fab up customs or midify BB Chevys to work. My truck is soley for street fun, no highway, no off road, no strip duty. 4.88 rear gears should help multiply torque as well as give new hope to tire shops in this uneasy economy! RPM, well, my right foot will have to manage that with those gears. Here's to stop lights and signs to keep me honest, and away from catastrophic motor failure. If I REALLY HAVE TOO, I'll re-install my 3.73s. No need to reply to that, let's stay focused on the exhaust.

So, what size pipes and mufflers will have a rumble that will shake the colagen out of your skin from 100 yards away? Low end Torque? I like it as much as everyone else, but with 500 cubes and 4.88s I'm not to worried about that in regards to pipe selection considerations. I really think that overall, the sound of the motor is what MOST concerns me, I want it to be LOUD, but not sound like a dump truck! Help me out, give me a hot rod (sounding) Caddy! Shoot those suggestions/sizes too me!