Re: 1957 18 h.p. parts
This is just my opinion:
I don't think it's worth it. YOu would be far better off keeping this FD-11 as a parts motor and buying yourself one for a cheap price and fixing it. The FD-11 and 12 are my favorite motors of all time, so keep in mind I say this hating to think of one being junked, but new pistons and such are very expensive. Also, there's a good chance that the crank journals and bearings could have rust, and I don't even know if you can get one new. If you could get the parts you needed and get new oversized pistons and get the block bored, you'd have far more in it that you would have going and buying a used motor in good shape. If you're patient, you can find a good one for around $200-$300, which is much less than you'd have in pistons, rings, and an overbore. You still may need bearings and a crank, which places you in used powerhead territory. A used powerhead may be a possibility, as I have seen used ones for sale pretty regularly in the past for reasonable prices.
Good luck,
JBJ