Forgive me for assuming this but the GT40 is beyond the reach of all of us. But perhaps there's a way to get in something around 40" tall with a V8 behind the seats for less than, say, a million. Find this 1965 Fiberfab Avenger GT for sale in Los Angeles, CA for $2,000 via craigslist.
No doubt, this is no small project. The first thing that needs to be done after it's on the road is correcting the square lazy eyes with some circular sealed beam lights and perspex headlight covers. After all, some artistic license is allowed when dealing with fiberglass of any kind.
Despite the unknown condition of the driveline and interior - we can assume really terrible - the body style is really attractive. Perhaps a few weekends of learning how to lay a gel coat could yield some dividends. Then later on you can spend your time researching Siano Corvair conversions and craigslisting up all the Weber IDF's and 327 small block parts you can find.
Matt, a self-proclaimed bottom-feeder of the classic car market, spends half of his time buying cars, half of his time retrieving them, and the remaining third on keeping them on the road.