Very few actual L1A1's were imported (if any) but there were quite a few L1A1 barrels and stocks attached to metric uppers and Inch lowers. (NOT that that is necessarily a bad thing.) The two major importers/mfg's I can think of were Hesse and Entreprise. Hesse didn't have a stellar reputation, Entreprise was occasionally spotty.
Entreprise usually had Type-3 uppers, less expensive than Type-1 or -2 because much less machining was done. You can see how plain the magazine well looks with no lightening cuts.
There are some advantages to Imperial/Inch FAL's (being that the UK looked at the Metric version and decided what they needed.)
1) The magazine release appears to be more clunky, requiring the left hand to release instead of just the right index finger. Requiring the left hand insures the magazine is easier to retain and not lost on the battlefield (it wasn't designed to be disposable like the AR magazine was).
2) The Inch safety is usually noted to be easier to reach than the Metric one.
3) Inch and Metric bolt hold opens are interchangeable, although most Inch bho's won't lock back it's an easy replacement.
4) If the receiver is actually Metric, metric magazines are much easier to obtain than Inch ones and will fit any magazine pouch interchangeably.
5) The Inch rear sight folds, which some people don't care for, there are companies that are making 'paratroop' rear sights for the L1A1. Someone has even adopted the H&K diopter sight to the FN
6) Inch upper receivers can accept the Canadian top cover which allows stripper clips to be used. Not that it's super useful, but it's fun to see an FAL that's completely open up top.
If at all in doubt if you have a Metric or Imperial receiver, check the photo below.
Imperial on the left has a big honkin' cut out for the magazine whereas the Metric has a dainty little half moon (which works just as well).