That is very clearly a major weld repair to the PTO. It may not break again, but it may not run true due to heat distortion. If you are doing a repair, you might as well run it and see how it goes, but if this is a restoration, the crankshaft is below standard in my opinion.
From your pictures of the rails, I'm not convinced that they are not cracked, welded, or both. You need pictures from above, front, back, and underneath, and from a lot closer up. Remember, that mower trashed its crankshaft, keyway, key and engine side clutch half from running out of balance. If the rails survived that, it would be remarkable. That is a pretty badly damaged mower.
