I have been looking for a good cheapo D2 as a parts car (but may also fix it later) for the main reason of rebuilding it's motor and drivetrain to then use in my existing 02.
I'm new and learning, so it's why I ask. I'd like to get a 4.6, ... but is the 4.0 a better choice?

 

That depends on whether or not you're going to have sleeves installed.

Personally, I'd take whichever came along first and just pin or weld the sleeves. That said, if I were not going to do that then I would get a 4.0 block. You can buy a 4.6 rotating assembly (crank and rods) and swap them into a 4.0 block. That will make it a 4.6.

 

So that's what a 4.6 is? Just a 4.0 with a longer stroke?
Same bore? Same sleeve issues?

 

Same bore, longer stroke, fewer sleeve issues but they still exist.