How much are we taking about?
[iAre you talking of replacing the 6 with an 8 ?f i was to do one what would i need?
If so you will need to change the front suspension.
What transmission will you be replacing with what???
If you think your gonna do this at home without the proper tools and equipment you need to think about even doing it your self.
You will need an engine hoist and a very good compressor with all of the air tools you think it will take. ( You really don't need a lift but having one will sure be nice.
You also will need $$$$$$$$ and knowledge.
Sorry, props to the original author "412 Horses", but about the best advise I saw on this topic over and over again.If you want a V8, buy a V8 car. It's always cheaper to buy it than build it in the long run. Been there, done that. Unless you can do the work yourself you're at the mercy of whoever is doing the work actually knowing how to do it, and what they charge you. And there's a good chance you'll ended up stuck in some hell world of somewhere in between with a big investment in parts and no running car to show for it. Financially you'll never come out ahead.
Plus, later when you want to sell the car no one is going to want to buy it at the price you are going to think it's worth after you've done all that work. And that's if you can even find anyone confident enough in the work to want it.