I've picked up a singer 51W56, well worn, missing a few small screws around the post, but very tight and in good condition internally.  Interesting to see one of those cotton/ string drive belts as used in the much later Singer 306. I understand a couple of you at least have done a needle bar conversion on similar machines?  I'm finding it hard to decide. My hook is in fine condition- so do I need to change the system?  I probably don't want to push the machine beyond M40/ Tex70 thread size/ siz