ebay chinese turbo kits are problematic. first, the turbos are usually cheaply made, you might be able to have a quality shop balance them and such to help them last a bit longer...second the headers are thin cheap poorly welded "stainless", almost all of them are knowf for cracking, warping, and leaking, there are some ebay stainless turbo headers that are better than others, but most of them at least need reinforcement on the turbo flange to support the weight of the turbos. i didn't go to the ebay link, but that kit picture doesn't show any exhaust piping, intake piping, and oil feed/return plumbing, not to mention an intercooler, which although it isn't a requirement, if you're running anything over like 6psi, you'll need one, and even if you're only running 6psi, you'll still want one. I also don't know if I'd trust ebay cheap no name wastegates too, you need something to control the boost really well, you don't want to get boost creep/etc....
also something to think about, even if you do get a quality twin turbo setup, there are ALOT of other issues you'll need to address right off the bat, for example: running forced induction on a 96+ vortec with the stock intake manifold, you WILL run out of fuel, period. so you'll also be investing in a marine intake or something else to get the proper amount of fuel, then there is PCM tuning which you'll need, and a mail order tune won't cut it, so you'll need to either pay for in person dyno tuning, or better yet get setup to tune the vehicle yourself, which may mean a PCM swap, wideband O2, etc. you'll be fabricating ALOT of stuff for it from intakes, to oil pathways to exhaust, intercooler stuff, so if you don't have a good welder (a TIG if you want to do anything quality with aluminum or stainless) then you'll need to find someone who does. then even once you have a bad ass quality boosted setup on the engine you'll have to think about the trans and rear end because that extra power and torque will tear apart a stock 60e and G80 rear in no time....
there is ALOT of work that goes into a proper twin turbo setup, I'm working on piecing one together, there is a link to my thread about it in my sig if you want to read about it, but it likely won't be finished for a while...