From what I have seen from my experience of owning a Ford 1100 which is your tractor's little brother (or since it is imcomplete, it's half brother, lol) you might seriously consider taking a serious inventory of what parts you have, and what you need. Purchase a shop manual with parts breakdown so you can see what isn't there. The parts I needed were often hard to find and very expensive to purchase when they were found in the normal channels. A rear axle was priced at over a thousand dollars ($US) but I ended up buying it from a dealer across the state (350 miles) for $237 that had it sitting on a shelf. Muffler is quoted at over $500 new but a used one was found for $60. How much of the original motor is there and what is wrong with it? Did somebody strip it to do some repair or is it unknown? A good engine shop "MIGHT" be able to look it over and give you some guidence about a rebuild. If the block is cracked, a good welder may be able to fix it, depends. I am seldom very good at diagonostics from across the room, much less across the big pond, so take everything with a grain of salt. Being a guy that collets way too much stuff for whatever project is at hand, I can understand wanting spares for EVERYHING, and usually in multiples, lol... but in your case, just getting the parts to put it back together is going to be a test. In fact, should you seriously consider wanting "spares" for everything, you might want to keep an eye out for a running 1900 and keep the spares you have right now for it.
David from jax