I know this is old, but I wanted to comment. I had one of the Navy Arms 66 carbines in 22 back in the late 70's. It was the most fun 22 Ive ever had. At one point I was shooting a case of 2500 rds a month through it. I never had any problems with it whatsoever, though it needed to taken apart and cleaned every now and then when it got sluggish cycling it. Of course I foolishly traded it off, and now would like to find another one, or a 73 carbine in 22. Id have no trepidation about parts.
BTW, I did make a 22 cal version of a Henry with mine, removing the forend and filing the boss off. I lost track of it, but would love to find it again.
When I bought mine, Navy Arms was advertising a package deal of guns that were probably slow sellers. It included the 22 cal 66, a 22 cal 73 carbine, 22 cal 73 trapper, 73 44-40 carbine, 1875 Rem copy, and a short barreled rolling block in 45-70. I couldn't afford to keep them all, the 66 was what I had the longest, though I wish Id kept one of the 73 22s.