Depends on you. I am competent enough to lets say, freshen my stock 302. For my 418, I had a friend assemble it who has a 950hp turbo car, and done dozens of motors. Why you may ask? Because with the money I spent on parts and machine work, I didnt want to overlook or screw anything up and ruin it all in a short amount of time. It cost alot of money anyway you do it, so choose the right parts the first time, even if you have to wait longer to scrape the money together. I've been without my car since about 6/03 because I sold the 302 to start the 418 project, but my moto has been "it's cheaper to do it once". Buy the right parts the first time. Good luck man.
mike.