@Evan Siegel, I don't know if you're still following this thread but if so, the reason why I asked what you mean about it not being clear how to implement GTD is that that could mean a number of different things. Are you struggling with what list manager to use, or what to put in your lists, or when to review them? Or something else entirely?
I realize that professionally, a "project" to you means a large, complex business undertaking. In GTD terms, a project is any outcome requiring two or more steps. That means a lot of your projects will be simple, straightforward endeavors requiring little, if any, planning. So using a tool like Microsoft Project to manage your GTD lists would be overkill.
When you're deciding what to do, all you really need are flat lists grouped together by the person, place or tool you'll need to accomplish those actions. You'll want a list of calls to make, a list of things you can do your computer, a list of errands to run, etc. These things don't need to be connected to their parent projects. When you're actually making calls, running errands, or what have you, you don't want to be distracted by also having to do higher-level thinking about the projects themselves. That's because using GTD, you'll have already done that thinking and decided that the actions you have in front of you are the right ones to review in that moment.
So if your struggle is with how to populate and manage these lists, you'll want to choose a tool that makes it easy to review and update your lists without forcing you to do higher-level project thinking every time you want to do something simple like make a call and cross it off your list. You could use paper, or a digital tool like the tasks feature in Outlook, or you could use one of the many other digital list managers out there.
Linking next actions to projects is a "nice to have" for some, but not a necessity. If you're reviewing your projects at least once per week, and capturing and clarifying inputs on a daily basis, you'll be able to keep your lists current with the actions necessary to achieve your desired outcomes.
If you do have projects that require more planning horsepower, you likely already have access to the tools needed to manage them. These sorts of things would be considered "project support" described by DA in the book. Project support should be kept distinctly separate from your next actions lists, and therefore there's no need for project support materials to be directly tied in to your GTD list manager. When you review your list of projects on a weekly basis, that will be the trigger to review project support materials if there are any that need reviewing.
As a salesperson, most of my professional projects are relatively simple. As I've said, I generally can't determine more than one or two next actions at a time for sales deals. On occasion, though, I have more complex projects like responding to Requests For Proposals (RFPs). Because I have to work with multiple people to get the information I need for such proposals, I often create fairly elaborate project plans in a spreadsheet or similar tool. The spreadsheet doesn't directly connect with the projects in my list manager. But when I see that project in the list during my weekly review, I am reminded to check the spreadsheet to see where everything stands.
I don't know if any of this helps. If not, feel free to speak up and help us understand what help you need.