Yeah, those holes are in just the right spot and aren't used in the other modes. It explains the size, shape and quantity of Octane's guns.
My feeling on him is that he sucks EXACTLY as much in comparison to the rest of the Classics figures as G1 Octane sucked in relation to the rest of the G1 figures of the same era...pretty much in the same ways...pretty much for the same reasons. I love the character though, so I'm happy to have him holding his rightful place of "Kinda vaguely cool, but only in the weakest reflected glory sort of way" in my classics collection So, in short, he's a perfect homage in every way, even more than a few unintended ones D/L
I like him. The shield staff thing appeals to my taste...in my classics universe, he is a warlord who is a fuel horder. Dunno why, makes him cooler in my book. I like his truck mode.
The smokestacks look is better on the Henkei version, since the guns are chromed. I always assumed that it was intentional also. Although I also think the truck is loosely based on the HEMTT M978 (very loosely), but I don't think the fact that that vehicle doesn't have smokestacks disproves it being intentional. I'm sure the designers wouldn't be above sticking in a nod to the G1 alt mode, even if it doesn't fit the type of truck that it's supposed to be. And you have the option of doing both anyway.