There was a period just prior to the flood of StG58 Kits when Century-made FrankenFALs were rather eclectic ... often an odd/interesting mixture of Inch & Metric parts (which explains the nickname ) ... but all of those that *I* have seen were built on Metric Uppers.My understanding is that they used the "L1A1" name rather loosely when most of the parts kit is from StG58, not L1A1.
OP, Go to Falfiles dot com. I learned how to build my FAL on that forum a decade ago, when 200 round battlepacks of 7.62 NATO were $30, and milspec mags were $6.
The Century angry beaver FALs usually take the more expensive inch pattern mags, and the ones with the unibrow feed ramp aren't exceptionally reliable. Century guns are NOT Imbel. Some may have been Coonan. Century guns can generally be made to run, if you are good with a dremel.
I built my FAL on an Imbel Gear Logo receiver, Chilean parts kit, Argentine chrome lined barrel, Penguin furniture amd FSE trigger group. It rocks & rolls. BTW, not all Imbels will have a gear logo.
There is a very good reason why FAL shooters keep gloves or an oven mitt in their gear bag...
I take it cast is almost as Imbel/Argie receivers.Cast receivers have a rougher surface finish and thicker dimensions.
I had DSA rebarrel an early L1A1 with an original uncut British barrel right after the ban expired.
Added US made guts, it turned out to be a very good shooter but I have no real love for FALs and sold it off.
ALL CAI L1A1 rifles use metric dimension receivers and use Metric magazines as far as I know.
Not a bad thing as long as the correct barrel locking shoulder is used and headspace maintained.
The British barrels are crush fit to the receivers but DSA proved they can be rebarrelled and the work completed better than the original build.
Not sure if DSA will still do this kind of work since they went all big time, contact and ask.