Seems rears up front is the the way to go. But the vortec im guessing weighs quite a bit more than the 4 banger. So you may need to add a few leaves to the spring pack.

The good thing about rears up front is its cheap, flexes like hell, and you already have them, or can come accross them easily. The only problem you will run into is the fact that the rears up front will move your axle foreward about an inch and a half, maybe even more, creating some strange steering issues if your running stock push pull.

I bet you can find a crossover setup on pirate or on this board if you keep your eyes peeled.

If you dont wanna go that rout im sure there are many stock lift springs around that some guys are getting rid of.