I have a 63 Original that I bought up in your area 15 yrs ago, somewhere between Greenville and Anderson. It has the original 7 hp Kohler and runs, everything there and functioning. I have seen some Cub Cadet originals that have had the 16 hp briggs v-twin engines installed on them and really like it. I have been tempted more than once to switch mine over but since it is an original in original condition I haven't done it. But if the right guy came along with a good v-twin, temptation MIGHT get the best of me.
On my parts list and diagrams CD about my original Cub Cadet, it lists the 7hp as being unavailable and lists the 8hp Kohler as being the replacement. So in your search, that too is another option.
Coincidentally, I rescued a Pennsylvania Panzer off of a load of scrap going to the shredder just last Friday, complete tractor, and it has the Kohler 8hp on it. Saw the guy maybe 2 miles from the scrap yard and knew where he was headed. Flagged him down and made a sweet lil deal.
I don't know how bad you want to keep your Original in original condition, but if it was me and I had one without the engine, I'd be looking for a nice lil v-twin to put in that booger. If you decide to do it, you have to cut the hood and make a neat lil adjustment to the sides but it is easy to do and turns out nice. It fits the original frame very well. The valve covers are slightly wider than the hood is the reason.
