In exactly the same way that the AKMS is a different rifle to the AKM.
As was the FAL Para.They were built with a folding stock as an OEM option,
Thanks.it didn't require major changes to the design as the receiver didn't extend into the stock to begin with.
And now PARAphrased, though just as accurate as the original:The FN Para was a different rifle from the regular fixed stock FAL. You can't just slap a Para stock onto a regular FAL, you need a Para receiver for it to go onto.
The AKMS was a different rifle from the regular fixed stock AKM. You can't just slap an AKMS stock onto a regular AKM, you need an AKMS receiver for it to go onto.