Yes with a carb & exhaust change. Unlike the engine in the 1971 GT HO Phase III, the 1971 Boss 351 was equipped with cast iron exhaust manifolds and an emissions carb. I've run a Boss 351 on a chassis dyno with the following changes:
Hi rpm points
Boss 302 Holley 780 carb, over the counter from Ford
Ford aluminum manifold for the Holley carburetor D1ZX-9425-DA
Headers grafted in to the factory exhaust system.
The car made 290 bhp at about 6000 rpm on the chassis dyno, which equates to about 370 bhp at the flywheel. That's with the factory mufflers which were rather restrictive, the water pump & power steering pump were running too. We could have squeezed a few more ponies out of it with a Shelby (Blue Thunder) intake manifold and Cadillac mufflers.
The car had 3.91:1 gears and a 4 speed top loader off the showroom floor, it was a nice strong running street car. It needed traction bars however. The engine ran just as strong with the factory "505" hydraulic cam too.