Thanks for all the comments/thoughts/feedback. This helmet has been sat on the side getting little attention for years as the WW2 stuff has been my main interest, so I've probably spent more time studying this helmet in the last 24 hours than in the last 7 or 8 years!
Obviously this is a controversial lid, but pending any other discoveries about it, I am 99% sure it is legit. On the downside is the good condition of the paintwork plus the handwriting on the inside - the paintwork seems to have been a "field done" job, so conceivably might
have been done not long before it was captured(?) and the writing could
have been done by the person who had the lid off the capturing soldier as opposed to by the soldier himself, as commented above. On the upside, this kind of helmet (though rare) does appear to have been used by Saddam's Iraq (examples sited above) and it has a slightly unique configuration that it shares with those other ones identified as being Iraqi (1980s style steel shell chin strap but clone type liner/strap).
At the start of the thread I thought it was possibly a US M1 or a Euro-clone of the M1 - I don't think it is either now - without being able to find any makers marks on it at all - and I have been over every inch of it today - my hunch is that it is something like South Korean made. Although the liner is plastic, it is not like the plastic Euro-clone liners (which I also have in my possession to compare) as apart from the fact they have a different feel about them (Euro liners have thicker/heavier and duller plastic than this), they also have a hole in the front for attaching insignia, like the WW2 fibre US ones did. This one does not. Below are some South Korean ROK Army M1's, presumably locally made - notice they have the same 1980s strap on the steel shell but the photos of the liners being worn at the DMZ show that the liners have no insignia hole in the front just like mine... So maybe S Korean made - like the M80 helmets were??
If only I could find someone to translate the Arabic - I might
have found someone for that, but it will be a few weeks before I can get hold of them...