@Drangir if he where just talking print store stuff, I recall there being a mild "random sizing issue" with the prints (I have not ordered any I just saw pics of a guy's two order of the robots being very diffrent in size). However he isn't
@Dennis Horne While its true that fitting the Cannon fodder arm on the Grogs likely isn't going happen for the two handed CF gun holds without conversion work, the grog guns seem to work just fine on the CF bodies once you know which arm goes to which hand:
And both set's arms seem to work okay with the bulldog bodies though the CF are a bit fiddlely "small arm in large socket" on the Bulldogs, however I blame this more on them being chunky monkey flavor torso sculpts, same deal with the grog issues you have (anyone telling you heroic is the “golden standard scale” is lying to you and most likely to themselves, Heroic proportions are all over the place 😆). I say this because thus far all the Death Fields gun arms I have come across IRL work great boltaction sculpts, I can stick pretty much any of the Death Feilds gun arms on Warlord Boltaction figures and they don't even look that out of place or "skipped leg day"ish.
Frankly though if your objective is a more "by the book IG look", given where you seem to be geographically based on your suggestion to me being in pounds, it might be wiser for you to just buy GW IG arms with the shoulder armor from your local ebay market in the grogs case (though the webbing may still get in the way) since one really does want some sort of shoulder pads with those grog sculpts anyways since they have a sad tendancy to look a little off without shoulder armor. With the Bulldogs you may want some to have a whole midsection replacement with a nice armored torso for that from the IG book look in addition to the guns (it does not have to be GW torso, plenty of matching third parties).
Also if I were to buy scratch build help parts from the UK, I would probably go with Ramshackle Games as my first choice just cuase they seem worth it price wise and back on topic have good range of vehicles that would likely work great with the Death Field minis, particularly the Damned though I am sure Ooh-rah could get some sweet ride too from them.
@JTam I think the Uzis are Sci-Fi box macs which makes more sense and works better with thier themeing, but okay😆.
A far future version of the "Build-A-Borz Practical Scrap Metal Small Arms Home workshop Machine Pistol" would be a good gun for them as well, it looks like a Sci Fi gun while also being something rednecks would build.