That's a $64,000 question. The answer depends upon your motivation, your skill, and the tools and assistance available to you.
For an unbiased look at installation effort, check out Teo Leonard's documentation of his build, which is ongoing. I like to say that it's about halfway between a Fiero-based kit (that is, one that doesn't require a wheelbase stretch) and a ground-up car like a Cobra. Your donor is already sitting on it's own suspension, and (if you don't do a swap) already has the drive train and wiring in place. If you can resist rebuilding every part of the donor car (which is tempting) you can have it together and ready for paint prep in 100 to 150 man-hours.
The customers who have built the VR range from those who have never turned a wrench before, but enjoy learning the skills as they go along, to those who are extremely experienced. I've seen very nice cars built by both extremes.
The Z is a uni-body car, so the installation process involves removing the roof, reinforcing the chassis, removing and replacing front-end components (bolt-on), trimming out the rear wheel wells and bonding on the rear tub. Obviously, there is a lot of smaller work, such as bolting on door mirrors, license plate, etc.
I strongly recommend that you get my Velo Rossa™ Installation Manual, the Jags That Run Z V8 book, the Haynes Z service book, and read them thoroughly. Then if you have more questions about the installation, email me and we'll clear them up before you begin.
The Daytona is similar to the VR in the way it installs.
The other kits I sell are to varying degrees easier than the VR and Daytona. Front-end components are all bolt-on or (in the case of racing applications) fastened with Dzus fasteners. Rear components are all bond-on, but can also be attached with Dzuz fasteners for racing.
The Z Spyder™ and ZX Spyder™ involve cutting off the roof (obviously), and like with the VR and Daytona reinforcing is always recommended when you remove the roof.
The 940Z ™, 280YZ™, and Subtle Z™ don't require removing the roof (though you can use parts from these kits on the Z Spyder™), so the installation is more simple. You also do not have to reinforce the donor car, but there will be a little trimming in the rear wheel well area to allow clearance for the larger wheels and tires you will want to use with these kits. If you (or your body shop) have installed fender flares before, any of these three kits should be pretty straight-forward for you.
I just published a free online fender kit installation guide that explains the process in more detail.
