There are several finished, or at least drivable V8 cars for sale right now in the classifieds all for around 10K.
After years of thinking about building one I finally decided I was ahead of the game to buy someone elses running project.
Sure I laid down some big coin up front, but I know I would have spent way more building the same car myself.
To address the original question...
It is a fairly well documented conversion. That being said there are 100's of ways to skin a cat.
A Chevy 350 crate motor is a great way to go since you get a brand new engine with about the best parts availability out there.
Don't forget that once you work out installing the engine, and plumbing a cooling system (that actually keeps the enging cool),
you'll quickly find other systems are lacking.
The one you'll read about again and again is the transaxle. The long and short of it...
The stock (901) transaxle will work, it can even survive for long periods and provide a good solution, IF you are easy on it.
For a much larger investment you can have more reliability by going with one of the beefier units such as the 915, 930, G50, ZF, or other exotic piece of unobtainium.
Now that you've dumped 300+ horspower into a 30-something year old car, how do you intend to stop it?
Upgraded brakes will become another addition to the parts list, as will beefier suspension and wheels.
...See how that money thing happens?...
If you do decide to build your own conversion then do your self a huge favor and shop for a clean 914 as a donor car. Not having to think about replacing the interior, replacing huge rusted chunks of the car, or repairing banged up body work will be worth it.
Welcome to the club and good luck!