Quoted: which fcg should I use?  It states on the website that the single hook fcg's don't work well with these receivers.  What options are there?  Is there anything I should look for when I get a parts kit.  I've been meaning to do this for at least a year. I finally have some extra money.

Go back to the listing for the NDS-3 receiver model and click through on the 'Troubleshooting' tab. Read through. Decide if you can do the necessary modifications if the single hook G2 fire control set has malfunctions. If you decide you can, then use the G2 single hook set. If you decide you cannot, then get the Arsenal single hook fire control set we offer. The Arsenal set can be sent with the receiver.

Harlan
NoDak Spud LLC

Quoted: The site looks interesting. What is the following? "top rail step-down"

Top rail step down is an emboss operation on the top rail that puts a step in the rail. The purpose of the extra step is to better fill the bolt carrier slot. This keeps the bolt carrier in better vertical alignment when tripping the auto sear. For semi auto function, the step down is not absolutely necessary.
Early AK's were mostly assembled on milled receivers. When the switch was made to a stamped sheet metal receiver, the designers wanted to keep the same spec for the bolt carrier slot, even though the top rail thickness on the stamped receiver is less than the thickness of the top rail on a milled receiver. In order to mimic the thickness found on the milled top rail, the designers of the stamped receiver added the 'top rail step down' emboss.

Harlan
NoDak Spud LLC