The different artist styles is indeed something I'm concerned about incorporating, as the big criticism of IDW is their constantly changing art/character/alt-mode styles. Flashbacks will help, which is why the Outback story might be easiest to get around that.
Lengthwise... stories can be condensed if you're careful, like using more dialogue than visual references. IDW suffers from padding out their issues/stories, so I would be looking at something that has the story of one IDW issue, but taking up a lot less pages, just to get to the point.

One other idea I didn't include was a total reboot, using Classics/Gen1 styles. It's a more recent story idea, so isn't fully worked out, but it was in response to how to contend with falling readership of the rather complex IDW universe now, in order to draw in new and old fans, who would rather see classic Gen1 that they are more familiar with. But the partial reboot of AHM seemed to also draw criticism... and I figured that a one-off comic here wouldn't be able to do it justice.

Besides, I like the idea of the Outback comic being able to use a character that IDW only introduced as a corpse, while also filling it with as much Aussie lingo as possible just to confuse any American readers who may stumble upon a copy in the future.