How hard is it?
Reasonably.
I looked into this before and found it was easier and cheaper to buy a v8.
Unless you had a smashed v8 with all the bits, the price of doing it properly would be
well over the price of a v8 in the first place.
You can get an engine and box cheap but all the small things add up, then you need to think
about the wiring side of things,brakes,driveline,cooling, rego etc... You could get one in and and get it running for cheapish,
but should you ever want to insure the car or sell it you could run into problems if not done properly.
As far as the swap goes It's just a matter of swapping parts. But in my opinion not worth the hassle.