The TY290 block does not include things like cylinder sleeves, bearing journals in fact I cant think of any wear sufraces that would be included. Unless there is a crack or hole in the old block, this is one part that is probably not needed. I suspect a crankshaft, bearing carriers (that bold into the block after bolting around the crankshaft), cylinder liners etc would be needed. Unfortunately the factory that made the 2 cyl TY engine folded about 4 years ago.
Tommy does have some 2 cylinder parts but complete engines are not available. Anticipating your next question: Since the block makes up part of the frame on a tractor, the mounting for the front axle will not match up with the 3 cyliner that replaced the 2 cylinder in the 20HP Jinma... Homier would be the best source for an engine but I doubt they have any...