you probably have Googled this by the time my reply comes up.
Featherweights are model 221, this is usually on the arm of the machine. Singer made a wood cart table that will hold a 221. they also made a very rare, oval table that the 221 sits in & stores in (even if you find this covered in paint-buy !)
mechanically, most 221s can be repaired. the gold decals can not be repaired without expensive re-painting. the 221 has a fold-up extension on the left end of the table. only 221 & 301 have this. this machine you are looking at is probably in a regular Singer cabinet that fits many, many machines. rarely do you see a 99 in the 3/4 size cabinet, but it if you do ! Spartan is just a 99 in a different dress. great machines,but heavier.
ISMACS is a great site for identity. also "Sandmans collectibles" on eBay has a really good ID site. Educate yourself so that if you do see a 221, you will be ready to jump. there are some real bargains to be had, but you need to be ready. I don't know how many 99s have been brought to us for repair of their "Featherweight". big $$ difference.