[zeke67]

One big thing to consider is the fuel system. You will need a sumped tank, high pressure lines, return lines, electric pump. There is an outfit out there that makes a front cover for LS engines that will allow use of a mechanical fuel pump and distributor, but that then puts you into a carburetor, so still not a drop in.

You can get them under the hood though. Some on here have done it, plus some of the magazines have too. Some floorpan modifications may be needed for the tranny, not sure if that's what you meant. Some frame notching may be needed too, depending on where the AC compressor needs to mount.

 

[zeke67]

It's the fuel tank that's going to get you. Most modern cars have the fuel tank up under the rear axle. So a donor vehicle tank isn't going to fit the Chevelle. Some one here did an LS swap and they used a B-body tank. They had to notch the rear frame rails to fit it, but at least it's a low cost donor option for an in tank electric pump.

I think you are also going to run into oil pan and accessory drive problems if you are going to try to do it with one vehicle. My sense is that it will take some mixing and matching, but you can still do it with OE stuff from junkyards.

Same is probably the true with exhaust manifolds. The same swap I mentioned used iron manifolds, but he had to go back to the junk yard and search around for ones that fit.