The only thing "completely safe" in terms of boost is none at all.
You can take the mildest 500-ish hp blower kit, tune it for crap and blow the whole shebang up.
Ford incorporated design thought into the block in terms of strong main webs, forged crank, etc. with an eye to boost at some point by somebody but, the majority of the rotating assembly, i.e. rods and pistons are N/A built. This does not mean to me your 5.0 is "built for boost". The fact that when you buy a Coyote from FRPP, you can spec it for FI or for NA, clarifies my point. FI drops static comp to 9.5:1 to allow more boost and way more power, more safely.
Centri blowers are the easiest and safest way to add boost. Easy install, simple tuning, boost is ramped with load (like a turbo) and they can be really responsive if you're careful and select a right sized head unit and step-up ratio.
I've tried every power adder out there, many on the same car, over the last few decades. I found centri to give the most smiles per hour. Were I given to do this on this car, which I'm not at this point, that's what I'd do, in a heartbeat.
