Be really careful with KA Fal/SLR internals. They're really hard to find parts for.
That been said I would probably do the gears and motor. It's a fairly standard V3 gearbox. 13:1 gears on a 16tpa motor should see it singing.
Don't mess with the hop doing flat hops ect as you will have real difficulty finding a replacement unit. I believe the Sig552 hop will fit, but I'm not sure of how good a fit it is.
Barrel wise I'd drop in something like a 6.03 ZCI if the KA has issues. If the KA one is good I'd just leave that in. And a good quality soft rubber bucking.
My shooting partner runs a KA L1A1 SLR. Basically the same gun with a slightly different look.
