Welcome to CHR - it is a great place for information and there's a lot of real deep hot rod talent here. We can also be pretty direct and ask tough questions - not to insult or hurt your feelings, but to help you define your project and help you get there and have some fun while you're at it!

I'm sure you're aware that the Datsun 510 V8 swap is not one of the easier transplants. Check out this web site and look carefully at the fit - Whacky Engine Swaps, Part II: Datzilla - Motor Trend Blog

Before you start yanking wrenches take some time to build a realistic budget. If this is your first effort, I can tell you that you will need a lot of help in terms of preparing the Datsun. The car was designed around a four cylinder and the V8 is not only heavier but it is physically a lot larger and there no easy way to get rid of the heat that the 327 will generate. To be successful, you'll literally have to build a custom chassis and drive train to set the 510 on.

As to the engine, search some of the threads here - we have this thrash several times a year re; building a SBC. I agree 100% with Lynn in terms of horsepower. 300 in a Datsun 510 would be killer - 500 horsepower is unrealistic unless you have a budget of $10,000 for the engine alone. Unless you have or work at a machine shop you will need to have a lot of the work done and the meter runs when you engage a quality shop. Read this article to learn how to make 500 horsepower from a 327 - 327 Small Block Chevy Engine Build - Chevy High Performance Magazine

Good luck on this one and again, welcome to CHR!
Glenn