Saying it's believable that a GLHS would be faster than a GN is like saying a 340 Dart Swinger would be faster than a solid-lifter 396 Chevelle. Is the A-body a giant-killer, capable of wreaking havoc on the Chevelle? Sure. But, all things being equal, it ain't faster than the L78.
The numbers don't lie. It may be hard to believe because you don't want to believe it, but I saw a lot of turbo Dodges put "muscle cars" to shame back in the day. Especially after a computer upgrade to increase the boost pressure. A $135 stage 1 computer would put that GLHS at 205 hp with a power to weight ratio of 11.2 lb/hp.
In 1986 Hot Rod magazine did an article to show how impressive the GLHS really was.
https://www.carmemories.com/cgi-bin/viewexperience.cgi?experience_id=113
