I would highly doubt that Callaway can fulfill orders for that kit based on the fact that the Rotomaster turbos are no longer available. That's a bummer about your financing. In the long run you will be better off with an '88 or newer car... maybe just wait as hard as that may be.
I would say more difficult than you realize if you want to do it correctly. Like any forced induction system, it is highly recommended that you drop compression on your car (and make sure that you have forged pistons), and go with a milder cam (than you would with a normally aspirated engine). Turbocharging is very hard on pistons (especially if you plan on adding NOS to this mix).
Another thing that you need to consider is where the turnochargers will be positioned underneath the car. If it is too close to the floorpan, you will run into some serious issues... like setting fire to your car.
You also want to invest on high quality waste gates, and pop-off valves. Don't scrimp on these components.
You should also research the types of turbochargers that would work best for your application(s). For road racing, you wuld probably go for a smaller unit with big intercooling. For drag racing you might go with a bigger turbocharger (like a pair of Garrett T-66 or T-88). They tend to have less turbo lag in comparison to the smaller units. The larger ones will not hold up as well in a road racing situationn at high prolonged rpm's.
The other issue is intercooling. If you choose not to intercool your turbocharged system, you will essentially lose half of your power increase when the car warms to running temperature (the same goes with non-intercooled supercharger systems). For big applications like V-8, it ii usually recommended that you use a air to water intercooler. This is where the costs go up on a system, and is a pretty critical component. You want to invest in the most robust intercooler that you can find.
Finally, I would highly recommend that you start this project with a fresh engine. Turbocharging will stress an engine quite a bit and many things that are worn can let go with the added stress.
The turbocharger experts can go on for hours on this subject alone. I personally am not a big fan of forced induction because of the durability issues that arise with them (versus normally aspirated engines). I hope that this helps. Good luck in your search.
Brad - Great post even if it wasn't the answer to the question. It would be awesome to find a comparable turbo for a swap. Especially since the Rotomaster T04B's that the '88-'91 TTs use are no longer made. It would need to have both oil and water line hookups and match up to the custom fabricated Callaway exhaust manifolds and intake lines from the Wonderbar and to the intercoolers. They would also have to clear all the parts like starter, frame rails, bell housing, etc. in that area. The Rotomasters use manual wastegates controlled with a screw.
It sounds like a very tall order. Any thoughts on something that might fit the bill?
I believe that it will be close to the T04. I will have to call and this out. I will post back here as soon as I find out. Keep in mind that it will also spool up faster than the T04 which will help. David thinks that the 87 can produce around 500hp if all is done correctly.
I eagerly await the findings.....If an 87 could be made to produce serious HP, that would make it easier to buy a car. Although I do know that the brakes and suspension were overhauled and upgraded in 88.