Or ask them to supply you with the correct A/C compressor for your 5.0. If your engine did not come with A/C, they can also supply you with the correct mounts and pulleys to make everything work like it came from the factory.
I like to use all new stuff just because I don't want to touch anything again for the next 150,000 miles. If the compressor fails, it makes a mess inside the system that has to be completely flushed. It's a real drag to have to fix.
I'd make a call to each of the three companies. Tell them what you have and what you want to do. Then place your order with the company you feel most comfortable with. All three companies make a very good product. In your case I would suggest buying direct, as the kit they put together for you will be custom, so any issues you may have can be solved in a single phone call.

Good luck!