All I've ever known is one engine for the 1967 GT500, the 428PI with 2x4 carburetion rated at 355hp. No single 4V that I've ever been aware of.The 1967 Shelby GT500 was the only year that had 2 offerings for the 428CI engine, one of which was the 355 BHP/420 TQ version with a single 4 BBL and the other was the 390 BHP/465 TQ version with dual 4 BBL's.
Also, for decades there's been arguments that Shelby factory-installed some 427's in GT500's. We all know about the one Super Snake. But some 427 low-risers and med risers were said to have been available for special order. THAT SAID, I'm pretty sure that all of those theories have been shot-down and attributed to dealer-installations instead. The 427 low-riser that was factory-installed in the 1968 Cougar GT-E was 390hp, FWIW. But I've never seen a Ford 428, of any code or iteration, rated at 390. And I've never seen a 1967 GT500 with a single carb. Even with factory a/c, still 2x4 induction. That was the standard setup.