if you are doing a stock 5.0 swap, it will be far cheaper to sell the 4 cyl car and put the money towards a running 5.0. a decent vehicle will run around 2-3k. the avg cost of the swap it well over a grand for just the parts unless you can get them dirt cheap. figure in time/labor/ and you are easily in the range of buying a gt outright.
the parts you will ABSOLUTELY need
computer
harness
engine
gas lines
radiator
K member
everything else should bolt up, but I highly suggest also swapping out the rear end, transmission, brakes, and suspension.
it's a huge job if you do it correctly.