Most hardback books these days have glued, rather than sewn, bindings. This means they’re basically paperbacks with hard covers. And because the covers are bigger than the book blocks, they slowly sag and pull their own spines out. Buy trade paperbacks instead.
For the first hundred years of its existence, Singer made sewing machines in lots of 10,000 to 50,000, so there are millions of any single model. Most cabinets are made to accept any head, with the exception of the 99, which is a 3/4 size machine, and the Featherweight.