I've got one of the older v twin Briggs engines that I got in a trade that had to holes in it about the size of a silver dollar. I broke some aluminum from another old blown engine and Tig ed it together with my wire welder and have been running it for several years now. I did have the extra parts such as rods etc in another engine or it would not have been practicle to do it.
Buy a new engine would be my suggestion.
I have one of those Zero turn Cub Cadets and I love it. It has about 1000 hours on it and I did a ring job on it a couple of years ago after it began to use oil and foul plugs. Other than that I've replaced the belts several times and cut a lot of grass. I love it!!!!!!!!!!!!!!!!!!