There is a part one, it's on their 2nd album and it's just called "Thoughts". There's also a "Part 4" on the Neal Morse album Momentum, which reprises elements of both songs. There is no part 3 for some reason, though there is a song called "Afterthoughts" on one of the post-Neal Spocks albums (though Neal wrote it). The song "Gibberish" on Day For Night is also another Gentle Giant inspired song. Morse loves that shit. And I can't say I blame him really. He does it well!
These are *intentional* Gentle Giant pastiches though (even the title: knots/thoughts). so I dunno if "ripoff" is even the right word to use here. though tbh I don't really care, like does Gentle Giant have a copyright on complex overlapping layered vocal parts? Any other band who's inspired by that is forever doomed to be a ripoff? It makes my ears perk up regardless of what band is doing it and more bands should do it if you ask me brooo.
But in general as you can hear they do have their own sound, the influences are undeniable but they obviously aren't trying to be "classic prog". Morse's songwriting is primarily pop-inspired. So his stuff doesn't really have much in the way of wanky instrumental solos or whatever. it's all very "songy". Which is what I like about them. Like Morse does have a lot of lengthy songs in his discography but they almost all feel to me like they have about the right equivalent number of shorter songs within them, it's really just a matter of whether the shorter pieces comprising it are good ones or not. So songs like "The Great Nothing" or "All Of The Above" don't really feel unnecessarily long or padded out in length to me, even though they're pushing 30 minutes.
Or maybe I've just destroyed all sense of time by listening to so many Phish and Dead concerts where a 20 minute jam feels like they've barely even gotten started man.