The downsides are close to the upsides on this one . May have to work on the disc brakes, but you will have disc brakes. I've seen disc brake kits for $400; if you want them , it'd be a good time to get them. Ls, cost varies, but you could save by buying the axle with Ls already , at least $100? Much stronger axles. The parasitic loss due to the extra weight of the parts will be almost unnoticeable. I'd cut the spring perches and shock mounts off a junk rear in a junkyard, and a decent welding shop could weld them on for you, for a reasonable price. If you were building up an axle anyway, this seems to give a good bang for the $.
02 edge 3.0 s/c manual 3.27 L/S, stock rims w 235 75 15's , e-fan mod , Underdog underdrive pulley , trac lock installed, hafta do somthing about those f-code t-bars