I have a somewhat unique opinion of the BOSS 302 engine.
First of all, for a factory-produced engine from back in '68, it was a pretty astounding offering. Great performance for that era, and with a factory warranty too!
With that being said, building or restoring an original BOSS 302 engine to factory specs would be a relatively expensive proposition...as compared to what a garden-variety 302 or 351 Windsor block could be built for using modern aftermarket parts.
The B2' engines were rated at 290 hp from Ford...most enthusiasts over the years feel that it is really closer to about 350 hp or so.
Now, that's in old-school, pre-SAE J1349-spec "gross" horsepower, which would be around 10% lower by today's SAE-net standards.
The true value of a B2 engine comes from it residing in it's original numbers-matching BOSS 302 ( or Cougar XR-7) body.
Putting an authentic B2 engine in a non numbers-matching Mustang ( or Cougar) will devalue the engine considerably. Putting that engine in a different model car altogether is basically a waste of the potential value of the engine in the propercar body.
If your goal is simply to have a rip-snortin' 302 that puts a smile on your face, could easily build a kick-ass 302 that will put any stock B2 engine on the trailer for far less of your money.
Plus, an all-original B2 engine is a relatively fragile and temperamental girl, requiring big octane. And the stock pistons are in effect high-speed hand-grenades.
So what am I saying? For collectabilty purposes, a B2 engine in B2 car is awesome.
For street-duty, a much-less expensive, more durable and more powerful 302/ 351 is a great choice.