It is legal, you'll need a US parts set (
www.tapco.com has FAL parts sets for $66-100 depending on quality) and a reciever to complete the build.
I built an FAL earlier this summer, the price of tools was pretty steep, but they're all reusable if I build another or I could sell them for a very small loss on
www.Falfiles.com The build only involved disassembly & cleaning of the parts kit, barreling the new reciever and setting headspace by changing locking shoulders (thats what needed all the tools) and reassembling the rest of the rifle around the newly barreled reciever (20 minute job) using the parts kit and the US parts from Tapco.
All told, the project cost:
$100 Tapco G1 parts kit (you'll probably never see one for this price again)
$100 US parts from Tapco (dont buy the $66 one that contains the Century trigger group unless you know what you're doing with the FAL)
$264 for reciever from FFL
$50 reciever wrench
$40 for .308 headspace gauges from Bushmaster (they stock FN/Forester .308 gauges)
$20 for pin gauges (they're used with the headspace gauges to determine what locking shoulder you need)
$30 for new locking shoulder (I wanted it immediately, so I bought one out-right with fast shipping, rather than trading the locking shoulder from my kit & paying a small fee for a new one)
$60 for DSA FAL tool kit (gas wrench, front sight wrench, buttstock/pistol grip wrench and extractor tool, all are VERY handy and the DSA quality is excellent, but you could make your own for less if you have a home shop with plans from Falfiles.com and you're the adventurous type)
G3-series builds are harder, I believe they require some welding and such. Not something I'd get into without knowing a lot more about.
If I see any more FAL kits for a reasonable price, I'll probably jump on one and save it for when I have the cash to do another build, my FAL's my new favorite rifle due to how simple it is to clean (brush & patch bore, spray some CLP on the reciever parts and wipe gas piston off with a paper towel) and its a just a little more (
) powerful than my ARs/poodle-shooters.
Kharn