The 99k is a really nice machine. Its a 3/4 size machine and is a "Baby 66". The big selling point for these machines were the fact that they were small and they would be perfect for the small flats that they have in the UK. Most of the time you see them as a portable but you will find them in the cabinets, and if you find a cabinet or treadle then its worth way more that the machine is!
All of the low shank feet will work and the standard Class 66 bobbins are used along with the 15x1 needles. Be sure to post photos of it so we all can enjoy your find!!
Billy