IMO those rear shock braces are a waste. Just look at it and try to imagine what good it is doing... There are much better things to help tighten up the rear...up to and including simply doing away with the entire 4 link setup. short of that a decent Panhard bar is a popular choice after you've done the upper and lower control arms and still want more control (which it sorely needs). Another option is a Watts Link. It's amazing to see a Watts Link on some SUVs, and the new Mustangs have a Panhard bar, but for us with the older Mustangs, we have to do it ourselves.
If fitment problems concern you (with FI), know that any bracer can be cut and re-welded to negotiate around the new hardware, but if it were me, I'd add the FI, then custom make my own brace. Not too difficult... (The latest Hot Rod magazine has a short 'how-to' article that maybe helpful...)
I'm big time jealous of your garage with a 70 Boss 302 in it. This (or the 69) was always a dream car for me. A buddy of mine had one back in high school (his Dad had bought it for him of course)...and back then they weren't $100K cars. Everything about the Boss 302 is just right. ENJOY and don't ever let it go!