Why would you pull out the 300 and install a V8? The 300 is one of the most awesome engines to put in an EB if done correctly.
The only swap I would consider is back to stock for authenticity. If you don't care about authenticity, leave the 300 and enjoy driving it.
That answered my question. I would have to sat this is the first that I have seen with the 300 in it and I know the 300 is an awesome engine. I will probably stick with it and just correct their crappy work. Hopefully In the next couple of weeks I will get to tearing it down and getting it back up to par