Inch (L1A1) kits:
- Welded tab on magazine is different from metric. Will not fit metric receiver. Metric mags will fit Inch receivers w/a little slop.
- Folding knob on charging handle. Folds forward to reduce snagging.
- Receiver is notched for charging handle knob.
- Feed ramp is slightly different.
- Barrel is indexed using shim washers to achieve 11:00 position.
- Pistol grip is attached to lower with a bolt instead of a permanent stud.
- Trigger guard can be removed to allow firing while wearing heavy gloves.
- Buttstock is different
- Receiver lock (allows lower and upper to separate) is different.
- Flash hider is different.
- Small notch in barrel for flash hider attachment.
- Gas regulator and gas block are different.
- Other minor differences.
Metric parts seem to be more plentiful. Both kits make great rifles, but receiver quality varies greatly by manufacturer. Check out opinions on other FAL boards before deciding on the brand of receiver to buy. I will HIGHLY recommend the DSA, but when you see the price (even the type 3) you'll scream. Imbel and Coonan are both good choices. Stay away from Williams and Century at all costs.
U.S. parts are available for both types, so compliance is not an issue. Both can be cut to carbine length and function fine.
The DSA top cover is unreal (again, you'll scream at the price)! It allows you to still use iron sights if you remove the scope. Some of the earlier top covers rendered iron sights useless because the rail was so tall. Tapco makes a couple of nice top covers too. One allows the use of stripper clips to charge the magazine (great for unfortunate Kalifornia residents).
Penguin stock sets are nice, and available in several colors. Gunthings had some nice walnut stock sets. Not cheap, but they are pretty.
Avoid the Century trigger group at all costs. That thing is turd-on-a-stick! The FSE trigger group is really nice, and would be my suggested piece. Tapco has a U.S. compliance parts set with a gas piston, charging handle, foregrip, and FSE trigger set for $99. The trigger set and piston go for $80, so why not get the other parts and save some cash.
I can post some pics of my Imbel-on-DSA if you want any details.