So back from the safe.
My letters:
1. 184 series, Kmini-14/5F shipped July 1983, which tells me stainless, folder, semi, 5 round mag.
2. 181 series, Mini-14/5F shipped Sept 1979, which tells me blue, folder, semi, 5 round mag.
3. 184 series, Mini-14/5F shipped Feb 1984, which tells me blue, folder, semi, 5 round mag.
4. 183 series, Mini-14/5F shipped Oct 1982, which tells me blue, folder, semi, 5 round mag.
5. 185 series, Mini-14/20GBK shipped Nov 1990, which tells me stainless Government w/ bayonet lug - and mine has a factory folding stock. Hmm.
6. 191 series, KAC556 shipped Feb 1984, which tells me only stainless FA. My gun has the 13" short barrel, stainless, factory folder. In my mind in a perfect world Ruger would have put on the letter "KAC556F"?, because I think KAC556 could mean fixed wood stock, 18.5" barrel. So either the clerk at Ruger forget the "F" or "K", Ruger's records are incorrect, or someone swapped both the barrel and stock on my KAC556. Or??? (Dan - your thoughts?)
Interesting in that Ruger appears to have stripped all reference to the 191- series AC556's from their website.