The question I asked myself was, would replica ridged G3 mudguards made in 2012 make a 1940 Matchless more original than the flat topped G3L mudguards that have probably been on it for the last 65 years? The change of mudguards is part of its history, but it's up to the individual and what you want from your finished machine, there is no right or wrong, just so long as you've got an old bike in the garage. If you are missing a part or it's too far gone to go back on, then that's fair enough, but I'm not bothered by the 'rivet counters', my Matchless looks great, goes like a train and sounds like the world is coming to an end, which is all that matters. 
Hi Bill..Niether of the mudguards you describe will make the bike 'original'..The new ribbed one, if that is the correct type, will only make it visually nearer to its original specification and the flat ones, although original guards, weren't originally fitted when the bike was manufactured.
However, only someone very familiar with Matchless specifications will notice the difference and if it doesn't bother you I would leave it like it is..These bikes are different things to different people..I just go with what I personally think is OK and suits my requirements whether that is 100% original or not..Original specification, after all, is optional not compulsory!. .Ian
email (option): ian@wright52.plus.com
That's the thing though isn't it Ian, there is a world of difference between original and original specification. I never said that the flat guards on mine were original, but they were probably fitted a very long time ago and by removing them to make the bike 'original spec' I think I'd be taking something away from its history? It can only be original once and when it's gone, can you recapture it by stripping the rest of its history away and fitting replica parts to get it back to its factory fresh appearence of 1940? It's up to the person who owns the bike and what you want to do with it when its done and I wouldn't say either approach is right or wrong, as you say, it's optional, not compulsory. I've nothing at all against changing a bikes wheels, tyres, tank, mudguards, seat and so on just to get it back to 'original spec', but it can sometimes be a bit like the old story of Cromwells dagger. It's been in the family for 300 years and only had two new blades and three new handles. I think if a bike is all still in once piece and shows evidence of several different incarnations, it's my personal view that trying to recapture the bikes original spec can sometimes detract from the finnished result. I can see this one running on a bit and perhaps we should just leave it and say that everyone is right as long as you ride them and don't just wrap them in cotton wool? 
Hey Bill, I've left the G3L guards on mine, after all they have been on there since 1946, which is longer than the originals were on. It all looks the part.
Cheers, Mick.
email (option): mick@motorbikemike.org.uk
Nice one Mick, lovely bike (nice tractor too!). That's my point exactly, well put. The ridged mudguards on your bike (and mine) were maybe there for just a couple of years, but the flat G3L ones have perhaps been in-situ for over 60 years. If they need replacing, then fair enopugh, but if they are still servicable, they are part of its history, why swap them for replicas just because that's what the rivet counters say? I believe there is another painting behind the Mona Lisa, but you wouldn't start scrubbing away with the turps just to make it 'original' would you? Actually, I hate that term 'rivet counters', very unfair and as I said previously, I actually can't see anything wrong with either approach, it's your bike and it's up to you, as long as you use it.
Hi Hinrik, originally all G3s and early G3ls were fitted with ribbed guards. The change happened sometime mid '42(perhaps someone can confirm the date). I also have a '41G3WO from the last contract. Heres a pic of the front guard that came with it. It could, of course, be an early G3L guard, but I would imagine the basic blade would have been the same-
The measurement from tip to tip along the rib is 930M/M.
Cheers, Mick.
email (option): mick@motorbikemike.org.uk