Normally I wouldn't be very enthusiastic about using 40k models for a different system, they are simply too intrinsically connected to the setting, but if there's one faction that could survive the transition it would be the Imperial Guard. Sure, the skulls and the grimdark are there, but not to such an extent as most of the other races. Of course I would like for the army to still be usable in 40k so there's that to consider too.
So looking at the army as it stands now (one platoon with four squads, a command squad and some stormtroopers) what I would like to add are some vehicles. I have another platoon command squad, some heavy weapons and a few more infantry here and there, but before painting those some vehicles would be nice. Making this into its own army I want to avoid any GW vehicles as those are what really make the army scream 40k. For the chimera at least I wanted something with wheels and as I was discussing my ideas on Twitter @hungryclone suggested the Chimera conversion kit from Chapterhouse Studios, putting wheels on it. But while the idea is interesting it simply looks... silly. The dimensions are all wrong, making it look more like a toy than a tank. I could see it as an Ork vehicle, but not for the guard, especially not my re-envisioned army.
Old Crow has a lot of nice stuff as well! The vehicles are generally a bit more "boxy looking" but in a way I quite like. The Claymore Heavy APC is the most obvious choice of course, but it might be a bit larger than what I had in mind. The different turret options are very nice though! The Trojan Light APC, clocking in at 115mm, is fairly small but I like the utalitarian look it has and you can't argue with the price! Speaking of size, what's the lenght of a Chimera? I tried to google it but couldn't find a good answer. Anyway, another Old Crow option (and the one I like the most) is to go with the Dragoon half track. It's 135mm long so a bit larger than the Trojan, but not as large as the Claymore or the Antenociti vehicles. It feels very fitting as the Steel Legion has a kind of space-nazi vibe to them, and it would certainly make for a unique looking force!
If I go with the Old Crow vehicles there are a number of different options for turret and weapon systems which should let me represent most of what is available for an Imperial Guard army (although I might have to forego sponsons on the Leman Russ).
Ironside from Pig Iron Productions is an alternative as well. Big and chunky is nice, although it doesn't have as many options available to it as the Old Crow stuff and it's tracked instead of wheeled. It's certainly the most 40k-ish looking of the bunch but also the priciest which is also something to take into consideration.
So, as you have probably figured out by now I'm leaning heavily towards Old Crow. While I do like the Antenociti vehicles better they don't fit as well as the Old Crow stuff. I think I'll reservere them for my Infinity table (and 15mm Mars of course!). However, I'm sure there are other manufacturers out there that I have forgotten. Would love to get my hands on the old Kamodo APC from DLD Productions, but they went under a few years back. So, any other neat sci-fi vehicles out there I should be aware of?
I might have written this as if I'm right about to put in an order, this is far from the truth though. This is one of my far, far, faaaaar off might-never-happen projects and is more of a thuught experiment than actual project. This might change of course, but don't hold your breath. :)