I have looked into it, deeply. It's definitely doable, cutting the firewall, moving the radiator forward... It will fit. The reason I'm not doing it is because it's around 120 pounds heavier than my 5.7 Hemi and will be too much forward weight on my car. I'm building a car for the twisties and that is far too much weight ahead of the spindle to maintain reasonable balance. If you look at a Viper chassis, the entire engine is behind the spindle center line. That's part of the reason the car is so balanced.
I can buy everything I need for my 5.7 Hemi, engine, controls, etc, build it to 500 HP, or whatever the Viper engine your looking at is, and have a more balanced, better performing car, for less money; typically (depends on the deal you can get on the engine). The only benefit I saw in the idea is the WOW factor when popping the hood.
This was a hard decision for me because the vision for my 69 Dart, is essentially a squared off Viper with a back seat. I'm using Viper suspension all around, trans, interior bits, etc, but it's just not worth the added weight in front for me.
Personal opinion here, if all your doing is going straight, doing car shows, or basic daily driving, it's not worth it. Even then, it's probably only best suited for car show duty. Just my .02.