I never ran the waggy springs, so I can't answer those questions...
I got the gears from a Nissan Junkyard in the Concord area. The guy's shop/jy is down the street behind the Lowes across the street from Concord Mills (on the right if you're going away from Lowes). Can't remember the name or a number, but I bought an entire rear axle from a 2004 Xterra (IIRC 2000-2004 had 4.9 gears from the factory) for $300 & scrapped the rest. I think the swap was worth it for the $$$, plus I think its kinda trick to have a pure Nissan axle (discs from a V6 pathy, gears from a Xterra & stock housing). That being said with 36" tires, I can't use 5th gear without a tailwind going downhill! If I break an axle, I'll use that as an excuse to go bigger & 5.XX gears...
I'm using teraflex revolver shackles in the rear that I had from the 3" suspension lift, I'm happy with them...
I don't know about the exhaust idea you've got...it would look pretty mean with some polished tips. But keep in mind how much stuff you throw in the bed and how much bed space you'll loose...that and any rain that could get into the exhaust while its just sitting outside.